HHH-16389 Introduce checkerframework for nullness marking/checking and null check the JPA metamodel generator

build.gradle

@@ -25,6 +25,8 @@ plugins {
 	id 'org.hibernate.orm.database-service' apply false
 	id 'biz.aQute.bnd' version '6.3.1' apply false
 
+	id 'org.checkerframework' version '0.6.25'
+
 	id 'io.github.gradle-nexus.publish-plugin' version '1.1.0'
 
 	id 'idea'

checkerstubs/jakarta.persistence.astub

@@ -0,0 +1,166 @@
+// Checkerframework stubs for the jakarta.persistence module
+
+package jakarta.persistence;
+
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+public interface AttributeConverter<X,Y> {
+	public @Nullable Y convertToDatabaseColumn(@Nullable X attribute);
+	public @Nullable X convertToEntityAttribute(@Nullable Y dbData);
+}
+public interface EntityManager extends AutoCloseable {
+	public <T> @Nullable T find(Class<T> entityClass, Object primaryKey);
+	public <T> @Nullable T find(Class<T> entityClass, Object primaryKey, Map<String, Object> properties);
+	public <T> @Nullable T find(Class<T> entityClass, Object primaryKey, LockModeType lockMode);
+	public <T> @Nullable T find(Class<T> entityClass, Object primaryKey, LockModeType lockMode, Map<String, Object> properties);
+}
+public interface EntityManagerFactory extends AutoCloseable {
+	public @Nullable Cache getCache();
+}
+public interface Parameter {
+	public @Nullable String getName();
+	public @Nullable Integer getPosition();
+}
+public interface PersistenceUnitUtil extends PersistenceUtil {
+	public @Nullable Object getIdentifier(Object entity);
+}
+public interface Query {
+	<T> Query setParameter(Parameter<T> param, @Nullable T value);
+	Query setParameter(Parameter<Calendar> param, @Nullable Calendar value, TemporalType temporalType);
+	Query setParameter(Parameter<Date> param, @Nullable Date value, TemporalType temporalType);
+	Query setParameter(String name, @Nullable Object value);
+	Query setParameter(String name, @Nullable Calendar value, TemporalType temporalType);
+	Query setParameter(String name, @Nullable Date value, TemporalType temporalType);
+	Query setParameter(int position, @Nullable Object value);
+	Query setParameter(int position, @Nullable Calendar value, TemporalType temporalType);
+	Query setParameter(int position, @Nullable Date value, TemporalType temporalType);
+	<T> @Nullable T getParameterValue(Parameter<T> param);
+	@Nullable Object getParameterValue(String name);
+	@Nullable Object getParameterValue(int position);
+}
+public interface StoredProcedureQuery extends Query {
+	<T> StoredProcedureQuery setParameter(Parameter<T> param, @Nullable T value);
+	StoredProcedureQuery setParameter(Parameter<Calendar> param, @Nullable Calendar value, TemporalType temporalType);
+	StoredProcedureQuery setParameter(Parameter<Date> param, @Nullable Date value, TemporalType temporalType);
+	StoredProcedureQuery setParameter(String name, @Nullable Object value);
+	StoredProcedureQuery setParameter(String name, @Nullable Calendar value, TemporalType temporalType);
+	StoredProcedureQuery setParameter(String name, @Nullable Date value, TemporalType temporalType);
+	StoredProcedureQuery setParameter(int position, @Nullable Object value);
+	StoredProcedureQuery setParameter(int position, @Nullable Calendar value, TemporalType temporalType);
+	StoredProcedureQuery setParameter(int position, @Nullable Date value, TemporalType temporalType);
+	@Nullable Object getOutputParameterValue(int position);
+	@Nullable Object getOutputParameterValue(String parameterName);
+}
+public interface TypedQuery<X> extends Query {
+	<T> TypedQuery<X> setParameter(Parameter<T> param, @Nullable T value);
+	TypedQuery<X> setParameter(Parameter<Calendar> param, @Nullable Calendar value, TemporalType temporalType);
+	TypedQuery<X> setParameter(Parameter<Date> param, @Nullable Date value, TemporalType temporalType);
+	TypedQuery<X> setParameter(String name, @Nullable Object value);
+	TypedQuery<X> setParameter(String name, @Nullable Calendar value, TemporalType temporalType);
+	TypedQuery<X> setParameter(String name, @Nullable Date value, TemporalType temporalType);
+	TypedQuery<X> setParameter(int position, @Nullable Object value);
+	TypedQuery<X> setParameter(int position, @Nullable Calendar value, TemporalType temporalType);
+	TypedQuery<X> setParameter(int position, @Nullable Date value, TemporalType temporalType);
+	@Nullable Object getOutputParameterValue(int position);
+	@Nullable Object getOutputParameterValue(String parameterName);
+}
+public interface Tuple {
+	<X> @Nullable X get(TupleElement<X> tupleElement);
+	<X> @Nullable X get(String alias, Class<X> type);
+	@Nullable Object get(String alias);
+	<X> @Nullable X get(int i, Class<X> type);
+	@Nullable Object get(int i);
+	@Nullable Object[] toArray();
+}
+public interface TupleElement<X> {
+	@Nullable String getAlias();
+}
+
+package jakarta.persistence.criteria;
+
+public interface CommonAbstractCriteria {
+	@Nullable Predicate getRestriction();
+}
+public interface AbstractQuery<T> extends CommonAbstractCriteria {
+	AbstractQuery<T> where(@Nullable Expression<Boolean> restriction);
+    AbstractQuery<T> where(@Nullable Predicate... restrictions);
+    AbstractQuery<T> having(@Nullable Expression<Boolean> restriction);
+    AbstractQuery<T> having(@Nullable Predicate... restrictions);
+	@Nullable Selection<T> getSelection();
+	@Nullable Predicate getGroupRestriction();
+}
+public interface CriteriaUpdate<T> extends CommonAbstractCriteria {
+	<Y, X extends Y> CriteriaUpdate<T> set(SingularAttribute<? super T, Y> attribute, @Nullable X value);
+	<Y, X extends Y> CriteriaUpdate<T> set(Path<Y> attribute, @Nullable X value);
+	CriteriaUpdate<T> set(String attributeName, @Nullable Object value);
+}
+public interface Subquery<T> extends AbstractQuery<T>, Expression<T> {
+	Subquery<T> where(@Nullable Expression<Boolean> restriction);
+    Subquery<T> where(@Nullable Predicate... restrictions);
+    Subquery<T> having(@Nullable Expression<Boolean> restriction);
+    Subquery<T> having(@Nullable Predicate... restrictions);
+	@Nullable Expression<T> getSelection();
+}
+public interface CriteriaBuilder {
+	public static interface SimpleCase<C,R> extends Expression<R> {
+		SimpleCase<C, R> when(C condition, @Nullable R result);
+		SimpleCase<C, R> when(Expression<? extends C> condition, @Nullable R result);
+		Expression<R> otherwise(@Nullable R result);
+	}
+	public static interface Case<R> extends Expression<R> {
+		Case<R> when(Expression<Boolean> condition, @Nullable R result);
+		Expression<R> otherwise(@Nullable R result);
+	}
+}
+public interface Join<Z, X> extends From<Z, X> {
+	Join<Z, X> on(@Nullable Expression<Boolean> restriction);
+    Join<Z, X> on(@Nullable Predicate... restrictions);
+    @Nullable Predicate getOn();
+}
+public interface SetJoin<Z,E> extends PluralJoin<Z, Set<E>, E> {
+	SetJoin<Z, E> on(@Nullable Expression<Boolean> restriction);
+    SetJoin<Z, E> on(@Nullable Predicate... restrictions);
+}
+public interface ListJoin<Z,E> extends PluralJoin<Z, List<E>, E> {
+	ListJoin<Z, E> on(@Nullable Expression<Boolean> restriction);
+    ListJoin<Z, E> on(@Nullable Predicate... restrictions);
+}
+public interface MapJoin<Z,K,V> extends PluralJoin<Z, Map<K,V>, V> {
+	MapJoin<Z,K,V> on(@Nullable Expression<Boolean> restriction);
+    MapJoin<Z,K,V> on(@Nullable Predicate... restrictions);
+}
+public interface Path<X> extends Expression<X> {
+	// CteRoot etc.
+	@Nullable Bindable<X> getModel();
+	@Nullable Path<?> getParentPath();
+    MapJoin<Z,K,V> on(@Nullable Predicate... restrictions);
+}
+
+package jakarta.persistence.metamodel;
+
+public interface IdentifiableType<X> extends ManagedType<X> {
+	@Nullable IdentifiableType<? super X> getSupertype();
+}
+
+package jakarta.persistence.spi;
+
+public interface ClassTransformer {
+	@Nullable byte[] transform(
+			@Nullable ClassLoader loader,
+			String className,
+			@Nullable Class<?> classBeingRedefined,
+			ProtectionDomain protectionDomain,
+			byte[] classfileBuffer) throws TransformerException;
+}
+public interface PersistenceProvider {
+	public @Nullable EntityManagerFactory createEntityManagerFactory(String emName, @Nullable Map map);
+	public EntityManagerFactory createContainerEntityManagerFactory(PersistenceUnitInfo info, @Nullable Map map);
+}
+public interface PersistenceUnitInfo {
+	public @Nullable String getPersistenceProviderClassName();
+	public @Nullable PersistenceUnitTransactionType getTransactionType();
+	public @Nullable DataSource getJtaDataSource();
+	public @Nullable DataSource getNonJtaDataSource();
+	public @Nullable ClassLoader getClassLoader();
+	public @Nullable ClassLoader getNewTempClassLoader();
+}

gradle/java-module.gradle

@@ -31,6 +31,8 @@ apply plugin: 'java-library'
 apply plugin: 'biz.aQute.bnd.builder'
 apply plugin: 'org.hibernate.orm.database-service'
 
+apply plugin: 'org.checkerframework'
+
 apply plugin: 'checkstyle'
 apply plugin: 'build-dashboard'
 apply plugin: 'project-report'
@@ -502,6 +504,9 @@ checkstyle {
 
 // exclude generated java sources - by explicitly setting the base source dir
 tasks.checkstyleMain.source = 'src/main/java'
+tasks.checkstyleMain
+		.exclude('org/hibernate/jpamodelgen/util/NullnessUtil.java')
+		.exclude('org/hibernate/internal/util/NullnessUtil.java')
 
 // define a second checkstyle task for checking non-fatal violations
 task nonFatalCheckstyle(type:Checkstyle) {
@@ -511,6 +516,17 @@ task nonFatalCheckstyle(type:Checkstyle) {
 	configFile = rootProject.file( 'shared/config/checkstyle/checkstyle-non-fatal.xml' )
 }
 
+checkerFramework {
+	checkers = [
+			'org.checkerframework.checker.nullness.NullnessChecker'
+	]
+	extraJavacArgs = [
+	        '-AsuppressWarnings=initialization',
+			"-Astubs=${project.rootDir}/checkerstubs",
+			'-AonlyDefs=^org\\.hibernate\\.jpamodelgen\\.'
+	]
+}
+
 
 task forbiddenApisSystemOut(type: CheckForbiddenApis, dependsOn: compileJava) {
 	bundledSignatures += 'jdk-system-out'

hibernate-core/src/main/java/org/hibernate/internal/util/NullnessUtil.java

@@ -0,0 +1,361 @@
+/*
+ * Checker Framework utilities
+ * Copyright 2004-present by the Checker Framework developers
+ *
+ * MIT License:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package org.hibernate.internal.util;
+
+import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.AnnotatedFor;
+
+/**
+ * Utility class for the Nullness Checker.
+ *
+ * <p>To avoid the need to write the NullnessUtil class name, do:
+ *
+ * <pre>import static org.checkerframework.checker.nullness.util.NullnessUtil.castNonNull;</pre>
+ * <p>
+ * or
+ *
+ * <pre>import static org.checkerframework.checker.nullness.util.NullnessUtil.*;</pre>
+ *
+ * <p><b>Runtime Dependency</b>: If you use this class, you must distribute (or link to) {@code
+ * checker-qual.jar}, along with your binaries. Or, you can copy this class into your own project.
+ */
+@SuppressWarnings({
+		"nullness", // Nullness utilities are trusted regarding nullness.
+		"cast" // Casts look redundant if Nullness Checker is not run.
+})
+@AnnotatedFor("nullness")
+public final class NullnessUtil {
+
+	private NullnessUtil() {
+		throw new AssertionError( "shouldn't be instantiated" );
+	}
+
+	/**
+	 * A method that suppresses warnings from the Nullness Checker.
+	 *
+	 * <p>The method takes a possibly-null reference, unsafely casts it to have the @NonNull type
+	 * qualifier, and returns it. The Nullness Checker considers both the return value, and also the
+	 * argument, to be non-null after the method call. Therefore, the {@code castNonNull} method can
+	 * be used either as a cast expression or as a statement. The Nullness Checker issues no warnings
+	 * in any of the following code:
+	 *
+	 * <pre><code>
+	 *   // one way to use as a cast:
+	 *  {@literal @}NonNull String s = castNonNull(possiblyNull1);
+	 *
+	 *   // another way to use as a cast:
+	 *   castNonNull(possiblyNull2).toString();
+	 *
+	 *   // one way to use as a statement:
+	 *   castNonNull(possiblyNull3);
+	 *   possiblyNull3.toString();`
+	 * </code></pre>
+	 * <p>
+	 * The {@code castNonNull} method is intended to be used in situations where the programmer
+	 * definitively knows that a given reference is not null, but the type system is unable to make
+	 * this deduction. It is not intended for defensive programming, in which a programmer cannot
+	 * prove that the value is not null but wishes to have an earlier indication if it is. See the
+	 * Checker Framework Manual for further discussion.
+	 *
+	 * <p>The method throws {@link AssertionError} if Java assertions are enabled and the argument is
+	 * {@code null}. If the exception is ever thrown, then that indicates that the programmer misused
+	 * the method by using it in a circumstance where its argument can be null.
+	 *
+	 * @param <T> the type of the reference
+	 * @param ref a reference of @Nullable type, that is non-null at run time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T castNonNull(@Nullable T ref) {
+		assert ref != null : "Misuse of castNonNull: called with a null argument";
+		return (@NonNull T) ref;
+	}
+
+	/**
+	 * Suppress warnings from the Nullness Checker, with a custom error message. See {@link
+	 * #castNonNull(Object)} for documentation.
+	 *
+	 * @param <T> the type of the reference
+	 * @param ref a reference of @Nullable type, that is non-null at run time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	public static @EnsuresNonNull("#1") <T extends @Nullable Object> @NonNull T castNonNull(
+			@Nullable T ref, String message) {
+		assert ref != null : "Misuse of castNonNull: called with a null argument: " + message;
+		return (@NonNull T) ref;
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [] castNonNullDeep(
+			T @Nullable [] arr) {
+		return (@NonNull T[]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [] castNonNullDeep(
+			T @Nullable [] arr, String message) {
+		return (@NonNull T[]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][] castNonNullDeep(
+			T @Nullable [] @Nullable [] arr) {
+		return (@NonNull T[][]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][] castNonNullDeep(
+			T @Nullable [] @Nullable [] arr, String message) {
+		return (@NonNull T[][]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (three levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] arr) {
+		return (@NonNull T[][][]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (three levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] arr, String message) {
+		return (@NonNull T[][][]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr) {
+		return (@NonNull T[][][][]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (four levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr, String message) {
+		return (@NonNull T[][][][]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (four levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr) {
+		return (@NonNull T[][][][][]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (five levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr, String message) {
+		return (@NonNull T[][][][][]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * The implementation of castNonNullDeep.
+	 *
+	 * @param <T> the component type (five levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if there is a non-null value, or null to use uncustomized
+	 * message
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 */
+	private static <T extends @Nullable Object> @NonNull T @NonNull [] castNonNullArray(
+			T @Nullable [] arr, @Nullable String message) {
+		assert arr != null
+				: "Misuse of castNonNullArray: called with a null array argument"
+				+ ( ( message == null ) ? "" : ( ": " + message ) );
+		for ( int i = 0; i < arr.length; ++i ) {
+			assert arr[i] != null
+					: "Misuse of castNonNull: called with a null array element"
+					+ ( ( message == null ) ? "" : ( ": " + message ) );
+			checkIfArray( arr[i], message );
+		}
+		return (@NonNull T[]) arr;
+	}
+
+	/**
+	 * If the argument is an array, requires it to be non-null at all levels.
+	 *
+	 * @param ref a value; if an array, all of its elements, and their elements recursively, are
+	 * non-null at run time
+	 * @param message text to include if there is a non-null value, or null to use uncustomized
+	 * message
+	 */
+	private static void checkIfArray(@NonNull Object ref, @Nullable String message) {
+		assert ref != null
+				: "Misuse of checkIfArray: called with a null argument"
+				+ ( ( message == null ) ? "" : ( ": " + message ) );
+		Class<?> comp = ref.getClass().getComponentType();
+		if ( comp != null ) {
+			// comp is non-null for arrays, otherwise null.
+			if ( comp.isPrimitive() ) {
+				// Nothing to do for arrays of primitive type: primitives are
+				// never null.
+			}
+			else {
+				castNonNullArray( (Object[]) ref, message );
+			}
+		}
+	}
+}

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/ClassWriter.java

@@ -27,6 +27,8 @@ import org.hibernate.jpamodelgen.model.MetaEntity;
 import org.hibernate.jpamodelgen.util.Constants;
 import org.hibernate.jpamodelgen.util.TypeUtils;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * Helper class to write the actual meta model class using the  {@link javax.annotation.processing.Filer} API.
  *
@@ -35,6 +37,8 @@ import org.hibernate.jpamodelgen.util.TypeUtils;
  */
 public final class ClassWriter {
 	private static final String META_MODEL_CLASS_NAME_SUFFIX = "_";
+	// See https://github.com/typetools/checker-framework/issues/979
+	@SuppressWarnings( "type.argument" )
 	private static final ThreadLocal<SimpleDateFormat> SIMPLE_DATE_FORMAT = new ThreadLocal<SimpleDateFormat>() {
 		@Override
 		public SimpleDateFormat initialValue() {
@@ -140,7 +144,7 @@ public final class ClassWriter {
 		pw.println( " {" );
 	}
 
-	private static String findMappedSuperClass(MetaEntity entity, Context context) {
+	private static @Nullable String findMappedSuperClass(MetaEntity entity, Context context) {
 		TypeMirror superClass = entity.getTypeElement().getSuperclass();
 		//superclass of Object is of NoType which returns some other kind
 		while ( superClass.getKind() == TypeKind.DECLARED ) {

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/Context.java

@@ -24,6 +24,8 @@ import org.hibernate.jpamodelgen.util.AccessType;
 import org.hibernate.jpamodelgen.util.AccessTypeInformation;
 import org.hibernate.jpamodelgen.util.Constants;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * @author Max Andersen
  * @author Hardy Ferentschik
@@ -68,21 +70,21 @@ public final class Context {
 	public Context(ProcessingEnvironment pe) {
 		this.pe = pe;
 
-		if ( pe.getOptions().get( JPAMetaModelEntityProcessor.PERSISTENCE_XML_OPTION ) != null ) {
+		String persistenceXmlOption = pe.getOptions().get( JPAMetaModelEntityProcessor.PERSISTENCE_XML_OPTION );
-			String tmp = pe.getOptions().get( JPAMetaModelEntityProcessor.PERSISTENCE_XML_OPTION );
+		if ( persistenceXmlOption != null ) {
-			if ( !tmp.startsWith( Constants.PATH_SEPARATOR ) ) {
+			if ( !persistenceXmlOption.startsWith( Constants.PATH_SEPARATOR ) ) {
-				tmp = Constants.PATH_SEPARATOR + tmp;
+				persistenceXmlOption = Constants.PATH_SEPARATOR + persistenceXmlOption;
 			}
-			persistenceXmlLocation = tmp;
+			persistenceXmlLocation = persistenceXmlOption;
 		}
 		else {
 			persistenceXmlLocation = DEFAULT_PERSISTENCE_XML_LOCATION;
 		}
 
-		if ( pe.getOptions().get( JPAMetaModelEntityProcessor.ORM_XML_OPTION ) != null ) {
+		String ormXmlOption = pe.getOptions().get( JPAMetaModelEntityProcessor.ORM_XML_OPTION );
-			String tmp = pe.getOptions().get( JPAMetaModelEntityProcessor.ORM_XML_OPTION );
+		if ( ormXmlOption != null ) {
-			ormXmlFiles = new ArrayList<String>();
+			ormXmlFiles = new ArrayList<>();
-			for ( String ormFile : tmp.split( "," ) ) {
+			for ( String ormFile : ormXmlOption.split( "," ) ) {
 				if ( !ormFile.startsWith( Constants.PATH_SEPARATOR ) ) {
 					ormFile = Constants.PATH_SEPARATOR + ormFile;
 				}
@@ -161,7 +163,7 @@ public final class Context {
 		return metaEntities.containsKey( fqcn );
 	}
 
-	public MetaEntity getMetaEntity(String fqcn) {
+	public @Nullable MetaEntity getMetaEntity(String fqcn) {
 		return metaEntities.get( fqcn );
 	}
 
@@ -177,7 +179,7 @@ public final class Context {
 		return metaEmbeddables.containsKey( fqcn );
 	}
 
-	public MetaEntity getMetaEmbeddable(String fqcn) {
+	public @Nullable MetaEntity getMetaEmbeddable(String fqcn) {
 		return metaEmbeddables.get( fqcn );
 	}
 
@@ -193,7 +195,7 @@ public final class Context {
 		accessTypeInformation.put( fqcn, info );
 	}
 
-	public AccessTypeInformation getAccessTypeInfo(String fqcn) {
+	public @Nullable AccessTypeInformation getAccessTypeInfo(String fqcn) {
 		return accessTypeInformation.get( fqcn );
 	}
 

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/JPAMetaModelEntityProcessor.java

@@ -36,6 +36,8 @@ import org.hibernate.jpamodelgen.util.StringUtil;
 import org.hibernate.jpamodelgen.util.TypeUtils;
 import org.hibernate.jpamodelgen.xml.JpaDescriptorParser;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * Main annotation processor.
  *
@@ -240,7 +242,7 @@ public class JPAMetaModelEntityProcessor extends AbstractProcessor {
 				requiresLazyMemberInitialization = true;
 			}
 
-			metaEntity = new AnnotationMetaEntity( (TypeElement) element, context, requiresLazyMemberInitialization );
+			metaEntity = AnnotationMetaEntity.create( (TypeElement) element, context, requiresLazyMemberInitialization );
 
 			if ( alreadyExistingMetaEntity != null ) {
 				metaEntity.mergeInMembers( alreadyExistingMetaEntity );
@@ -249,7 +251,7 @@ public class JPAMetaModelEntityProcessor extends AbstractProcessor {
 		}
 	}
 
-	private MetaEntity tryGettingExistingEntityFromContext(AnnotationMirror mirror, String fqn) {
+	private @Nullable MetaEntity tryGettingExistingEntityFromContext(AnnotationMirror mirror, String fqn) {
 		MetaEntity alreadyExistingMetaEntity = null;
 		if ( TypeUtils.isAnnotationMirrorOfType( mirror, Constants.ENTITY )
 				|| TypeUtils.isAnnotationMirrorOfType( mirror, Constants.MAPPED_SUPERCLASS )) {

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/Version.java

@@ -6,20 +6,24 @@
  */
 package org.hibernate.jpamodelgen;
 
+import org.hibernate.jpamodelgen.util.NullnessUtil;
+
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * Information about the Meta Model Generator version.
  *
  * @author Hardy Ferentschik
  */
 public final class Version {
-	private static String version;
+	private static @Nullable String version;
 
 	private Version() {
 	}
 
 	public static String getVersionString() {
 		if ( version == null ) {
-			version = Version.class.getPackage().getImplementationVersion();
+			version = NullnessUtil.castNonNull( Version.class.getPackage() ).getImplementationVersion();
 			if ( version == null ) {
 				version = "[WORKING]";
 			}

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/annotation/AnnotationMetaEntity.java

@@ -28,6 +28,7 @@ import org.hibernate.jpamodelgen.model.MetaEntity;
 import org.hibernate.jpamodelgen.util.AccessType;
 import org.hibernate.jpamodelgen.util.AccessTypeInformation;
 import org.hibernate.jpamodelgen.util.Constants;
+import org.hibernate.jpamodelgen.util.NullnessUtil;
 import org.hibernate.jpamodelgen.util.TypeUtils;
 
 /**
@@ -66,14 +67,19 @@ public class AnnotationMetaEntity implements MetaEntity {
 	 */
 	private MetaEntity entityToMerge;
 
-	public AnnotationMetaEntity(TypeElement element, Context context, boolean lazilyInitialised) {
+	public AnnotationMetaEntity(TypeElement element, Context context) {
 		this.element = element;
 		this.context = context;
-		this.members = new HashMap<String, MetaAttribute>();
+		this.members = new HashMap<>();
-		this.importContext = new ImportContextImpl( getPackageName() );
+		this.importContext = new ImportContextImpl( getPackageName( context, element ) );
+	}
+
+	public static AnnotationMetaEntity create(TypeElement element, Context context, boolean lazilyInitialised) {
+		final AnnotationMetaEntity annotationMetaEntity = new AnnotationMetaEntity( element, context );
 		if ( !lazilyInitialised ) {
-			init();
+			annotationMetaEntity.init();
 		}
+		return annotationMetaEntity;
 	}
 
 	public AccessTypeInformation getEntityAccessTypeInfo() {
@@ -93,6 +99,10 @@ public class AnnotationMetaEntity implements MetaEntity {
 	}
 
 	public final String getPackageName() {
+		return getPackageName( context, element );
+	}
+
+	private static String getPackageName(Context context, TypeElement element) {
 		PackageElement packageOf = context.getElementUtils().getPackageOf( element );
 		return context.getElementUtils().getName( packageOf.getQualifiedName() ).toString();
 	}
@@ -167,7 +177,8 @@ public class AnnotationMetaEntity implements MetaEntity {
 		getContext().logMessage( Diagnostic.Kind.OTHER, "Initializing type " + getQualifiedName() + "." );
 
 		TypeUtils.determineAccessTypeForHierarchy( element, context );
-		entityAccessTypeInfo = context.getAccessTypeInfo( getQualifiedName() );
+		AccessTypeInformation accessTypeInfo = context.getAccessTypeInfo( getQualifiedName() );
+		entityAccessTypeInfo = NullnessUtil.castNonNull(accessTypeInfo);
 
 		List<? extends Element> fieldsOfClass = ElementFilter.fieldsIn( element.getEnclosedElements() );
 		addPersistentMembers( fieldsOfClass, AccessType.FIELD );

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/annotation/MetaAttributeGenerationVisitor.java

@@ -25,13 +25,16 @@ import org.hibernate.jpamodelgen.Context;
 import org.hibernate.jpamodelgen.util.AccessType;
 import org.hibernate.jpamodelgen.util.AccessTypeInformation;
 import org.hibernate.jpamodelgen.util.Constants;
+import org.hibernate.jpamodelgen.util.NullnessUtil;
 import org.hibernate.jpamodelgen.util.StringUtil;
 import org.hibernate.jpamodelgen.util.TypeUtils;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * @author Hardy Ferentschik
  */
-public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<AnnotationMetaAttribute, Element> {
+public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<@Nullable AnnotationMetaAttribute, Element> {
 
 	/**
 	 * FQCN of the Hibernate-specific {@code @Target} annotation.
@@ -54,12 +57,12 @@ public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<Annotatio
 	}
 
 	@Override
-	public AnnotationMetaAttribute visitPrimitive(PrimitiveType t, Element element) {
+	public @Nullable AnnotationMetaAttribute visitPrimitive(PrimitiveType t, Element element) {
 		return new AnnotationMetaSingleAttribute( entity, element, TypeUtils.toTypeString( t ) );
 	}
 
 	@Override
-	public AnnotationMetaAttribute visitArray(ArrayType t, Element element) {
+	public @Nullable AnnotationMetaAttribute visitArray(ArrayType t, Element element) {
 		// METAGEN-2 - For now we handle arrays as SingularAttribute
 		// The code below is an attempt to be closer to the spec and only allow byte[], Byte[], char[] and Character[]
 //			AnnotationMetaSingleAttribute attribute = null;
@@ -81,7 +84,7 @@ public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<Annotatio
 	}
 
 	@Override
-	public AnnotationMetaAttribute visitTypeVariable(TypeVariable t, Element element) {
+	public @Nullable AnnotationMetaAttribute visitTypeVariable(TypeVariable t, Element element) {
 		// METAGEN-29 - for a type variable we use the upper bound
 		TypeMirror mirror = t.getUpperBound();
 		TypeMirror erasedType = context.getTypeUtils().erasure( mirror );
@@ -91,7 +94,7 @@ public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<Annotatio
 	}
 
 	@Override
-	public AnnotationMetaAttribute visitDeclared(DeclaredType declaredType, Element element) {
+	public @Nullable AnnotationMetaAttribute visitDeclared(DeclaredType declaredType, Element element) {
 		AnnotationMetaAttribute metaAttribute = null;
 		TypeElement returnedElement = (TypeElement) context.getTypeUtils().asElement( declaredType );
 		// WARNING: .toString() is necessary here since Name equals does not compare to String
@@ -110,7 +113,7 @@ public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<Annotatio
 		return metaAttribute;
 	}
 
-	private AnnotationMetaAttribute createMetaCollectionAttribute(DeclaredType declaredType, Element element, String fqNameOfReturnType, String collection, String targetEntity) {
+	private @Nullable AnnotationMetaAttribute createMetaCollectionAttribute(DeclaredType declaredType, Element element, String fqNameOfReturnType, String collection, @Nullable String targetEntity) {
 		if ( TypeUtils.containsAnnotation( element, Constants.ELEMENT_COLLECTION ) ) {
 			String explicitTargetEntity = getTargetEntity( element.getAnnotationMirrors() );
 			TypeMirror collectionElementType = TypeUtils.getCollectionElementType(
@@ -164,7 +167,7 @@ public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<Annotatio
 	}
 
 	@Override
-	public AnnotationMetaAttribute visitExecutable(ExecutableType t, Element p) {
+	public @Nullable AnnotationMetaAttribute visitExecutable(ExecutableType t, Element p) {
 		if ( !p.getKind().equals( ElementKind.METHOD ) ) {
 			return null;
 		}
@@ -196,13 +199,12 @@ public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<Annotatio
 		return returnedElement.asType().accept( basicVisitor, returnedElement );
 	}
 
-	private AnnotationMetaAttribute createAnnotationMetaAttributeForMap(DeclaredType declaredType, Element element, String collection, String targetEntity) {
+	private @Nullable AnnotationMetaAttribute createAnnotationMetaAttributeForMap(DeclaredType declaredType, Element element, String collection, @Nullable String targetEntity) {
+		final AnnotationMirror annotationMirror = TypeUtils.getAnnotationMirror( element, Constants.MAP_KEY_CLASS );
 		String keyType;
-		if ( TypeUtils.containsAnnotation( element, Constants.MAP_KEY_CLASS ) ) {
+		if ( annotationMirror != null ) {
-			TypeMirror typeMirror = (TypeMirror) TypeUtils.getAnnotationValue(
+			TypeMirror typeMirror = (TypeMirror) NullnessUtil.castNonNull(
-					TypeUtils.getAnnotationMirror(
+					TypeUtils.getAnnotationValue( annotationMirror, TypeUtils.DEFAULT_ANNOTATION_PARAMETER_NAME )
-							element, Constants.MAP_KEY_CLASS
-					), TypeUtils.DEFAULT_ANNOTATION_PARAMETER_NAME
 			);
 			keyType = typeMirror.toString();
 		}
@@ -218,7 +220,7 @@ public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<Annotatio
 		);
 	}
 
-	private String getElementType(DeclaredType declaredType, String targetEntity) {
+	private String getElementType(DeclaredType declaredType, @Nullable String targetEntity) {
 		if ( targetEntity != null ) {
 			return targetEntity;
 		}
@@ -247,7 +249,7 @@ public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<Annotatio
 	 *
 	 * @return target entity class name as string or {@code null} if no targetEntity is here or if equals to void
 	 */
-	private String getTargetEntity(List<? extends AnnotationMirror> annotations) {
+	private @Nullable String getTargetEntity(List<? extends AnnotationMirror> annotations) {
 		String fullyQualifiedTargetEntityName = null;
 		for ( AnnotationMirror mirror : annotations ) {
 			if ( TypeUtils.isAnnotationMirrorOfType( mirror, Constants.ELEMENT_COLLECTION ) ) {
@@ -266,7 +268,7 @@ public class MetaAttributeGenerationVisitor extends SimpleTypeVisitor6<Annotatio
 		return fullyQualifiedTargetEntityName;
 	}
 
-	private String getFullyQualifiedClassNameOfTargetEntity(AnnotationMirror mirror, String parameterName) {
+	private @Nullable String getFullyQualifiedClassNameOfTargetEntity(AnnotationMirror mirror, String parameterName) {
 		assert mirror != null;
 		assert parameterName != null;
 
@@ -291,6 +293,7 @@ class BasicAttributeVisitor extends SimpleTypeVisitor6<Boolean, Element> {
 	private final Context context;
 
 	public BasicAttributeVisitor(Context context) {
+		super( Boolean.FALSE );
 		this.context = context;
 	}
 

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/util/AccessTypeInformation.java

@@ -6,6 +6,8 @@
  */
 package org.hibernate.jpamodelgen.util;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * Encapsulates the access type information for a single class.
  *
@@ -17,17 +19,17 @@ public class AccessTypeInformation {
 	/**
 	 * Access type explicitly specified in xml or on an entity.
 	 */
-	private AccessType explicitAccessType;
+	private @Nullable AccessType explicitAccessType;
 
 	/**
 	 * The default type for en entity. This type might change during the parsing/discovering process. The reason
 	 * for that is the ability to mix and match xml and annotation configuration.
 	 */
-	private AccessType defaultAccessType;
+	private @Nullable AccessType defaultAccessType;
 
 	private static final AccessType DEFAULT_ACCESS_TYPE = AccessType.PROPERTY;
 
-	public AccessTypeInformation(String fqcn, AccessType explicitAccessType, AccessType defaultAccessType) {
+	public AccessTypeInformation(String fqcn, @Nullable AccessType explicitAccessType, @Nullable AccessType defaultAccessType) {
 		this.fqcn = fqcn;
 		this.explicitAccessType = explicitAccessType;
 		this.defaultAccessType = defaultAccessType;
@@ -58,7 +60,7 @@ public class AccessTypeInformation {
 		this.explicitAccessType = explicitAccessType;
 	}
 
-	public AccessType getDefaultAccessType() {
+	public @Nullable AccessType getDefaultAccessType() {
 		return defaultAccessType;
 	}
 

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/util/FileTimeStampChecker.java

@@ -10,6 +10,8 @@ import java.io.Serializable;
 import java.util.HashMap;
 import java.util.Map;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * @author Hardy Ferentschik
  */
@@ -26,7 +28,7 @@ public class FileTimeStampChecker implements Serializable {
 	}
 
 	@Override
-	public boolean equals(Object o) {
+	public boolean equals(@Nullable Object o) {
 		if ( this == o ) {
 			return true;
 		}

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/util/NullnessUtil.java

@@ -0,0 +1,361 @@
+/*
+ * Checker Framework utilities
+ * Copyright 2004-present by the Checker Framework developers
+ *
+ * MIT License:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package org.hibernate.jpamodelgen.util;
+
+import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.AnnotatedFor;
+
+/**
+ * Utility class for the Nullness Checker.
+ *
+ * <p>To avoid the need to write the NullnessUtil class name, do:
+ *
+ * <pre>import static org.checkerframework.checker.nullness.util.NullnessUtil.castNonNull;</pre>
+ * <p>
+ * or
+ *
+ * <pre>import static org.checkerframework.checker.nullness.util.NullnessUtil.*;</pre>
+ *
+ * <p><b>Runtime Dependency</b>: If you use this class, you must distribute (or link to) {@code
+ * checker-qual.jar}, along with your binaries. Or, you can copy this class into your own project.
+ */
+@SuppressWarnings({
+		"nullness", // Nullness utilities are trusted regarding nullness.
+		"cast" // Casts look redundant if Nullness Checker is not run.
+})
+@AnnotatedFor("nullness")
+public final class NullnessUtil {
+
+	private NullnessUtil() {
+		throw new AssertionError( "shouldn't be instantiated" );
+	}
+
+	/**
+	 * A method that suppresses warnings from the Nullness Checker.
+	 *
+	 * <p>The method takes a possibly-null reference, unsafely casts it to have the @NonNull type
+	 * qualifier, and returns it. The Nullness Checker considers both the return value, and also the
+	 * argument, to be non-null after the method call. Therefore, the {@code castNonNull} method can
+	 * be used either as a cast expression or as a statement. The Nullness Checker issues no warnings
+	 * in any of the following code:
+	 *
+	 * <pre><code>
+	 *   // one way to use as a cast:
+	 *  {@literal @}NonNull String s = castNonNull(possiblyNull1);
+	 *
+	 *   // another way to use as a cast:
+	 *   castNonNull(possiblyNull2).toString();
+	 *
+	 *   // one way to use as a statement:
+	 *   castNonNull(possiblyNull3);
+	 *   possiblyNull3.toString();`
+	 * </code></pre>
+	 * <p>
+	 * The {@code castNonNull} method is intended to be used in situations where the programmer
+	 * definitively knows that a given reference is not null, but the type system is unable to make
+	 * this deduction. It is not intended for defensive programming, in which a programmer cannot
+	 * prove that the value is not null but wishes to have an earlier indication if it is. See the
+	 * Checker Framework Manual for further discussion.
+	 *
+	 * <p>The method throws {@link AssertionError} if Java assertions are enabled and the argument is
+	 * {@code null}. If the exception is ever thrown, then that indicates that the programmer misused
+	 * the method by using it in a circumstance where its argument can be null.
+	 *
+	 * @param <T> the type of the reference
+	 * @param ref a reference of @Nullable type, that is non-null at run time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T castNonNull(@Nullable T ref) {
+		assert ref != null : "Misuse of castNonNull: called with a null argument";
+		return (@NonNull T) ref;
+	}
+
+	/**
+	 * Suppress warnings from the Nullness Checker, with a custom error message. See {@link
+	 * #castNonNull(Object)} for documentation.
+	 *
+	 * @param <T> the type of the reference
+	 * @param ref a reference of @Nullable type, that is non-null at run time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	public static @EnsuresNonNull("#1") <T extends @Nullable Object> @NonNull T castNonNull(
+			@Nullable T ref, String message) {
+		assert ref != null : "Misuse of castNonNull: called with a null argument: " + message;
+		return (@NonNull T) ref;
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [] castNonNullDeep(
+			T @Nullable [] arr) {
+		return (@NonNull T[]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [] castNonNullDeep(
+			T @Nullable [] arr, String message) {
+		return (@NonNull T[]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][] castNonNullDeep(
+			T @Nullable [] @Nullable [] arr) {
+		return (@NonNull T[][]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][] castNonNullDeep(
+			T @Nullable [] @Nullable [] arr, String message) {
+		return (@NonNull T[][]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (three levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] arr) {
+		return (@NonNull T[][][]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (three levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] arr, String message) {
+		return (@NonNull T[][][]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr) {
+		return (@NonNull T[][][][]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (four levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr, String message) {
+		return (@NonNull T[][][][]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (four levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr) {
+		return (@NonNull T[][][][][]) castNonNullArray( arr, null );
+	}
+
+	/**
+	 * Like castNonNull, but whereas that method only checks and casts the reference itself, this
+	 * traverses all levels of the argument array. The array is recursively checked to ensure that all
+	 * elements at every array level are non-null.
+	 *
+	 * @param <T> the component type (five levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if this method is misused
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 *
+	 * @see #castNonNull(Object)
+	 */
+	@EnsuresNonNull("#1")
+	public static <T extends @Nullable Object> @NonNull T @NonNull [][][][][] castNonNullDeep(
+			T @Nullable [] @Nullable [] @Nullable [] @Nullable [] @Nullable [] arr, String message) {
+		return (@NonNull T[][][][][]) castNonNullArray( arr, message );
+	}
+
+	/**
+	 * The implementation of castNonNullDeep.
+	 *
+	 * @param <T> the component type (five levels in) of the array
+	 * @param arr an array all of whose elements, and their elements recursively, are non-null at run
+	 * time
+	 * @param message text to include if there is a non-null value, or null to use uncustomized
+	 * message
+	 *
+	 * @return the argument, casted to have the type qualifier @NonNull at all levels
+	 */
+	private static <T extends @Nullable Object> @NonNull T @NonNull [] castNonNullArray(
+			T @Nullable [] arr, @Nullable String message) {
+		assert arr != null
+				: "Misuse of castNonNullArray: called with a null array argument"
+				+ ( ( message == null ) ? "" : ( ": " + message ) );
+		for ( int i = 0; i < arr.length; ++i ) {
+			assert arr[i] != null
+					: "Misuse of castNonNull: called with a null array element"
+					+ ( ( message == null ) ? "" : ( ": " + message ) );
+			checkIfArray( arr[i], message );
+		}
+		return (@NonNull T[]) arr;
+	}
+
+	/**
+	 * If the argument is an array, requires it to be non-null at all levels.
+	 *
+	 * @param ref a value; if an array, all of its elements, and their elements recursively, are
+	 * non-null at run time
+	 * @param message text to include if there is a non-null value, or null to use uncustomized
+	 * message
+	 */
+	private static void checkIfArray(@NonNull Object ref, @Nullable String message) {
+		assert ref != null
+				: "Misuse of checkIfArray: called with a null argument"
+				+ ( ( message == null ) ? "" : ( ": " + message ) );
+		Class<?> comp = ref.getClass().getComponentType();
+		if ( comp != null ) {
+			// comp is non-null for arrays, otherwise null.
+			if ( comp.isPrimitive() ) {
+				// Nothing to do for arrays of primitive type: primitives are
+				// never null.
+			}
+			else {
+				castNonNullArray( (Object[]) ref, message );
+			}
+		}
+	}
+}

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/util/TypeRenderingVisitor.java

@@ -26,10 +26,12 @@ import javax.lang.model.type.UnionType;
 import javax.lang.model.type.WildcardType;
 import javax.lang.model.util.SimpleTypeVisitor8;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * @author Christian Beikov
  */
-public final class TypeRenderingVisitor extends SimpleTypeVisitor8<Object, Object> {
+public final class TypeRenderingVisitor extends SimpleTypeVisitor8<@Nullable Object, @Nullable Object> {
 
 	private final StringBuilder sb = new StringBuilder();
 	private final Set<TypeVariable> visitedTypeVariables = new HashSet<>();
@@ -66,7 +68,7 @@ public final class TypeRenderingVisitor extends SimpleTypeVisitor8<Object, Objec
 	}
 
 	@Override
-	public Object visitPrimitive(PrimitiveType t, Object o) {
+	public @Nullable Object visitPrimitive(PrimitiveType t, @Nullable Object o) {
 		final String primitiveTypeName = getPrimitiveTypeName( t.getKind() );
 		if ( primitiveTypeName != null ) {
 			sb.append( primitiveTypeName );
@@ -74,7 +76,7 @@ public final class TypeRenderingVisitor extends SimpleTypeVisitor8<Object, Objec
 		return null;
 	}
 
-	private static String getPrimitiveTypeName(TypeKind kind) {
+	private static @Nullable String getPrimitiveTypeName(TypeKind kind) {
 		switch ( kind ) {
 			case INT:
 				return "int";
@@ -99,19 +101,19 @@ public final class TypeRenderingVisitor extends SimpleTypeVisitor8<Object, Objec
 	}
 
 	@Override
-	public Object visitNull(NullType t, Object o) {
+	public @Nullable Object visitNull(NullType t, @Nullable Object o) {
 		return null;
 	}
 
 	@Override
-	public Object visitArray(ArrayType t, Object o) {
+	public @Nullable Object visitArray(ArrayType t, @Nullable Object o) {
 		t.getComponentType().accept( this, null );
 		sb.append( "[]" );
 		return t;
 	}
 
 	@Override
-	public Object visitDeclared(DeclaredType t, Object o) {
+	public @Nullable Object visitDeclared(DeclaredType t, @Nullable Object o) {
 		sb.append( t.asElement().toString() );
 		List<? extends TypeMirror> typeArguments = t.getTypeArguments();
 		if ( !typeArguments.isEmpty() ) {
@@ -127,7 +129,7 @@ public final class TypeRenderingVisitor extends SimpleTypeVisitor8<Object, Objec
 	}
 
 	@Override
-	public Object visitTypeVariable(TypeVariable t, Object o) {
+	public @Nullable Object visitTypeVariable(TypeVariable t, @Nullable Object o) {
 		final Element typeVariableElement = t.asElement();
 		if ( typeVariableElement instanceof TypeParameterElement ) {
 			final TypeParameterElement typeParameter = (TypeParameterElement) typeVariableElement;
@@ -145,7 +147,7 @@ public final class TypeRenderingVisitor extends SimpleTypeVisitor8<Object, Objec
 	}
 
 	@Override
-	public Object visitWildcard(WildcardType t, Object o) {
+	public @Nullable Object visitWildcard(WildcardType t, @Nullable Object o) {
 		sb.append( '?' );
 		if ( t.getExtendsBound() != null ) {
 			sb.append( " extends " );
@@ -159,12 +161,12 @@ public final class TypeRenderingVisitor extends SimpleTypeVisitor8<Object, Objec
 	}
 
 	@Override
-	public Object visitUnion(UnionType t, Object o) {
+	public @Nullable Object visitUnion(UnionType t, @Nullable Object o) {
 		return null;
 	}
 
 	@Override
-	public Object visitIntersection(IntersectionType t, Object o) {
+	public @Nullable Object visitIntersection(IntersectionType t, @Nullable Object o) {
 		final List<? extends TypeMirror> bounds = t.getBounds();
 		bounds.get( 0 ).accept( this, null );
 		for ( int i = 0; i < bounds.size(); i++ ) {
@@ -175,12 +177,12 @@ public final class TypeRenderingVisitor extends SimpleTypeVisitor8<Object, Objec
 	}
 
 	@Override
-	public Object visitExecutable(ExecutableType t, Object o) {
+	public @Nullable Object visitExecutable(ExecutableType t, @Nullable Object o) {
 		return null;
 	}
 
 	@Override
-	public Object visitNoType(NoType t, Object o) {
+	public @Nullable Object visitNoType(NoType t, @Nullable Object o) {
 		return null;
 	}
 }

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/util/TypeUtils.java

@@ -31,6 +31,8 @@ import javax.tools.Diagnostic;
 import org.hibernate.jpamodelgen.Context;
 import org.hibernate.jpamodelgen.MetaModelGenerationException;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * Utility class.
  *
@@ -72,7 +74,7 @@ public final class TypeUtils {
 
 	public static String toTypeString(TypeMirror type) {
 		if ( type.getKind().isPrimitive() ) {
-			return PRIMITIVE_WRAPPERS.get( type.getKind() );
+			return NullnessUtil.castNonNull( PRIMITIVE_WRAPPERS.get( type.getKind() ) );
 		}
 		return TypeRenderingVisitor.toString( type );
 	}
@@ -102,7 +104,7 @@ public final class TypeUtils {
 		return extractClosestRealTypeAsString( component, context ) + "[]";
 	}
 
-	public static TypeElement getSuperclassTypeElement(TypeElement element) {
+	public static @Nullable TypeElement getSuperclassTypeElement(TypeElement element) {
 		final TypeMirror superClass = element.getSuperclass();
 		//superclass of Object is of NoType which returns some other kind
 		if ( superClass.getKind() == TypeKind.DECLARED ) {
@@ -175,7 +177,7 @@ public final class TypeUtils {
 	 * @return the annotation mirror for the specified annotation class from the {@code Element} or {@code null} in case
 	 *         the {@code TypeElement} does not host the specified annotation.
 	 */
-	public static AnnotationMirror getAnnotationMirror(Element element, String fqcn) {
+	public static @Nullable AnnotationMirror getAnnotationMirror(Element element, String fqcn) {
 		assert element != null;
 		assert fqcn != null;
 
@@ -189,7 +191,7 @@ public final class TypeUtils {
 		return mirror;
 	}
 
-	public static Object getAnnotationValue(AnnotationMirror annotationMirror, String parameterValue) {
+	public static @Nullable Object getAnnotationValue(AnnotationMirror annotationMirror, String parameterValue) {
 		assert annotationMirror != null;
 		assert parameterValue != null;
 
@@ -251,7 +253,7 @@ public final class TypeUtils {
 		updateEmbeddableAccessType( searchedElement, context, defaultAccessType );
 	}
 
-	public static TypeMirror getCollectionElementType(DeclaredType t, String fqNameOfReturnedType, String explicitTargetEntityName, Context context) {
+	public static TypeMirror getCollectionElementType(DeclaredType t, String fqNameOfReturnedType, @Nullable String explicitTargetEntityName, Context context) {
 		TypeMirror collectionElementType;
 		if ( explicitTargetEntityName != null ) {
 			Elements elements = context.getElementUtils();
@@ -300,7 +302,7 @@ public final class TypeUtils {
 		}
 	}
 
-	private static AccessType getDefaultAccessForHierarchy(TypeElement element, Context context) {
+	private static @Nullable AccessType getDefaultAccessForHierarchy(TypeElement element, Context context) {
 		AccessType defaultAccessType = null;
 		TypeElement superClass = element;
 		do {
@@ -370,7 +372,7 @@ public final class TypeUtils {
 	 * @return returns the access type of the element annotated with the id annotation. If no element is annotated
 	 *         {@code null} is returned.
 	 */
-	private static AccessType getAccessTypeInCaseElementIsRoot(TypeElement searchedElement, Context context) {
+	private static @Nullable AccessType getAccessTypeInCaseElementIsRoot(TypeElement searchedElement, Context context) {
 		List<? extends Element> myMembers = searchedElement.getEnclosedElements();
 		for ( Element subElement : myMembers ) {
 			List<? extends AnnotationMirror> entityAnnotations =
@@ -385,7 +387,7 @@ public final class TypeUtils {
 		return null;
 	}
 
-	private static AccessType getAccessTypeOfIdAnnotation(Element element) {
+	private static @Nullable AccessType getAccessTypeOfIdAnnotation(Element element) {
 		AccessType accessType = null;
 		final ElementKind kind = element.getKind();
 		if ( kind == ElementKind.FIELD || kind == ElementKind.METHOD ) {
@@ -399,13 +401,12 @@ public final class TypeUtils {
 				|| TypeUtils.isAnnotationMirrorOfType( annotationMirror, Constants.EMBEDDED_ID );
 	}
 
-	public static AccessType determineAnnotationSpecifiedAccessType(Element element) {
+	public static @Nullable AccessType determineAnnotationSpecifiedAccessType(Element element) {
 		final AnnotationMirror accessAnnotationMirror = TypeUtils.getAnnotationMirror( element, Constants.ACCESS );
 		AccessType forcedAccessType = null;
 		if ( accessAnnotationMirror != null ) {
-			Element accessElement = (Element) TypeUtils.getAnnotationValue(
+			Element accessElement = (Element) NullnessUtil.castNonNull(
-					accessAnnotationMirror,
+					TypeUtils.getAnnotationValue( accessAnnotationMirror, DEFAULT_ANNOTATION_PARAMETER_NAME )
-					DEFAULT_ANNOTATION_PARAMETER_NAME
 			);
 			if ( accessElement.getKind().equals( ElementKind.ENUM_CONSTANT ) ) {
 				if ( accessElement.getSimpleName().toString().equals( AccessType.PROPERTY.toString() ) ) {
@@ -436,7 +437,7 @@ public final class TypeUtils {
 		return extractClosestRealTypeAsString( typeArguments.get( 0 ), context );
 	}
 
-	static class EmbeddedAttributeVisitor extends SimpleTypeVisitor6<String, Element> {
+	static class EmbeddedAttributeVisitor extends SimpleTypeVisitor6<@Nullable String, Element> {
 		private Context context;
 
 		EmbeddedAttributeVisitor(Context context) {
@@ -444,7 +445,7 @@ public final class TypeUtils {
 		}
 
 		@Override
-		public String visitDeclared(DeclaredType declaredType, Element element) {
+		public @Nullable String visitDeclared(DeclaredType declaredType, Element element) {
 			TypeElement returnedElement = (TypeElement) context.getTypeUtils().asElement( declaredType );
 			String fqNameOfReturnType = null;
 			if ( containsAnnotation( returnedElement, Constants.EMBEDDABLE ) ) {
@@ -454,7 +455,7 @@ public final class TypeUtils {
 		}
 
 		@Override
-		public String visitExecutable(ExecutableType t, Element p) {
+		public @Nullable String visitExecutable(ExecutableType t, Element p) {
 			if ( !p.getKind().equals( ElementKind.METHOD ) ) {
 				return null;
 			}

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/util/xml/JpaNamespaceTransformingEventReader.java

@@ -131,10 +131,10 @@ public class JpaNamespaceTransformingEventReader extends EventReaderDelegate {
 	}
 
 	private List<Namespace> updateElementNamespaces(StartElement startElement) {
-		List<Namespace> newNamespaceList = new ArrayList<Namespace>();
+		List<Namespace> newNamespaceList = new ArrayList<>();
-		Iterator<?> existingNamespaceIterator = startElement.getNamespaces();
+		Iterator<Namespace> existingNamespaceIterator = startElement.getNamespaces();
 		while ( existingNamespaceIterator.hasNext() ) {
-			Namespace namespace = (Namespace) existingNamespaceIterator.next();
+			Namespace namespace = existingNamespaceIterator.next();
 			if ( NAMESPACE_MAPPING.containsKey( namespace.getNamespaceURI() ) ) {
 				newNamespaceList.add( xmlEventFactory.createNamespace( EMPTY_PREFIX, currentDocumentNamespaceUri ) );
 			}
@@ -153,10 +153,10 @@ public class JpaNamespaceTransformingEventReader extends EventReaderDelegate {
 
 	private List<Attribute> updateElementAttributes(StartElement startElement) {
 		// adjust the version attribute
-		List<Attribute> newElementAttributeList = new ArrayList<Attribute>();
+		List<Attribute> newElementAttributeList = new ArrayList<>();
-		Iterator<?> existingAttributesIterator = startElement.getAttributes();
+		Iterator<Attribute> existingAttributesIterator = startElement.getAttributes();
 		while ( existingAttributesIterator.hasNext() ) {
-			Attribute attribute = (Attribute) existingAttributesIterator.next();
+			Attribute attribute = existingAttributesIterator.next();
 			if ( VERSION_ATTRIBUTE_NAME.equals( attribute.getName().getLocalPart() ) ) {
 				if ( currentDocumentNamespaceUri.equals( DEFAULT_PERSISTENCE_NAMESPACE ) ) {
 					if ( !DEFAULT_PERSISTENCE_VERSION.equals( attribute.getName().getPrefix() ) ) {

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/util/xml/XmlParserHelper.java

@@ -24,8 +24,10 @@ import javax.xml.validation.SchemaFactory;
 
 import org.hibernate.jpamodelgen.Context;
 import org.hibernate.jpamodelgen.util.Constants;
+import org.hibernate.jpamodelgen.util.NullnessUtil;
 import org.hibernate.jpamodelgen.xml.jaxb.ObjectFactory;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
 import org.xml.sax.SAXException;
 
 /**
@@ -48,7 +50,7 @@ public class XmlParserHelper {
 
 	private static final XMLInputFactory XML_INPUT_FACTORY = XMLInputFactory.newInstance();
 
-	private static final ConcurrentMap<String, Schema> SCHEMA_CACHE = new ConcurrentHashMap<String, Schema>(
+	private static final ConcurrentMap<String, Schema> SCHEMA_CACHE = new ConcurrentHashMap<>(
 			NUMBER_OF_SCHEMAS
 	);
 
@@ -66,7 +68,7 @@ public class XmlParserHelper {
 	 *
 	 * @return an input stream for the specified resource or {@code null} in case resource cannot be loaded
 	 */
-	public InputStream getInputStreamForResource(String resource) {
+	public @Nullable InputStream getInputStreamForResource(String resource) {
 		// METAGEN-75
 		if ( !resource.startsWith( RESOURCE_PATH_SEPARATOR ) ) {
 			resource = RESOURCE_PATH_SEPARATOR + resource;
@@ -160,19 +162,17 @@ public class XmlParserHelper {
 	}
 
 	private Schema loadSchema(String schemaName) throws XmlParsingException {
-		Schema schema = null;
+		URL schemaUrl = NullnessUtil.castNonNull( this.getClass().getClassLoader() ).getResource( schemaName );
-		URL schemaUrl = this.getClass().getClassLoader().getResource( schemaName );
 		if ( schemaUrl == null ) {
-			return schema;
+			throw new IllegalArgumentException( "Couldn't find schema on classpath: " + schemaName );
 		}
 
 		SchemaFactory sf = SchemaFactory.newInstance( javax.xml.XMLConstants.W3C_XML_SCHEMA_NS_URI );
 		try {
-			schema = sf.newSchema( schemaUrl );
+			return sf.newSchema( schemaUrl );
 		}
 		catch ( SAXException e ) {
 			throw new XmlParsingException( "Unable to create schema for " + schemaName + ": " + e.getMessage(), e );
 		}
-		return schema;
 	}
 }

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/xml/JpaDescriptorParser.java

@@ -38,6 +38,8 @@ import org.hibernate.jpamodelgen.xml.jaxb.Persistence;
 import org.hibernate.jpamodelgen.xml.jaxb.PersistenceUnitDefaults;
 import org.hibernate.jpamodelgen.xml.jaxb.PersistenceUnitMetadata;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * Parser for JPA XML descriptors (persistence.xml and referenced mapping files).
  *
@@ -105,7 +107,7 @@ public class JpaDescriptorParser {
 		return mappingFileNames;
 	}
 
-	private Persistence getPersistence() {
+	private @Nullable Persistence getPersistence() {
 		Persistence persistence = null;
 		String persistenceXmlLocation = context.getPersistenceXmlLocation();
 		final InputStream stream = xmlParserHelper.getInputStreamForResource( persistenceXmlLocation );
@@ -249,7 +251,7 @@ public class JpaDescriptorParser {
 				continue;
 			}
 
-			XmlMetaEntity metaEntity = new XmlMetaEntity(
+			XmlMetaEntity metaEntity = XmlMetaEntity.create(
 					entity, defaultPackageName, getXmlMappedType( fqcn ), context
 			);
 			if ( context.containsMetaEntity( fqcn ) ) {
@@ -333,8 +335,9 @@ public class JpaDescriptorParser {
 
 	private AccessType determineEntityAccessType(EntityMappings mappings) {
 		AccessType accessType = context.getPersistenceUnitDefaultAccessType();
-		if ( mappings.getAccess() != null ) {
+		final org.hibernate.jpamodelgen.xml.jaxb.AccessType mappingsAccess = mappings.getAccess();
-			accessType = mapXmlAccessTypeToJpaAccessType( mappings.getAccess() );
+		if ( mappingsAccess != null ) {
+			accessType = mapXmlAccessTypeToJpaAccessType( mappingsAccess );
 		}
 		return accessType;
 	}
@@ -456,15 +459,11 @@ public class JpaDescriptorParser {
 
 	private AccessType mapXmlAccessTypeToJpaAccessType(org.hibernate.jpamodelgen.xml.jaxb.AccessType xmlAccessType) {
 		switch ( xmlAccessType ) {
-			case FIELD: {
+			case FIELD:
 				return AccessType.FIELD;
-			}
+			case PROPERTY:
-			case PROPERTY: {
 				return AccessType.PROPERTY;
-			}
-			default: {
-			}
 		}
-		return null;
+		throw new IllegalArgumentException( "Unknown access type: " + xmlAccessType );
 	}
 }

tooling/metamodel-generator/src/main/java/org/hibernate/jpamodelgen/xml/XmlMetaEntity.java

@@ -26,6 +26,7 @@ import org.hibernate.jpamodelgen.model.ImportContext;
 import org.hibernate.jpamodelgen.model.MetaAttribute;
 import org.hibernate.jpamodelgen.model.MetaEntity;
 import org.hibernate.jpamodelgen.util.AccessTypeInformation;
+import org.hibernate.jpamodelgen.util.NullnessUtil;
 import org.hibernate.jpamodelgen.util.StringUtil;
 import org.hibernate.jpamodelgen.util.TypeUtils;
 import org.hibernate.jpamodelgen.xml.jaxb.Attributes;
@@ -44,6 +45,8 @@ import org.hibernate.jpamodelgen.xml.jaxb.MappedSuperclass;
 import org.hibernate.jpamodelgen.xml.jaxb.OneToMany;
 import org.hibernate.jpamodelgen.xml.jaxb.OneToOne;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * Collects XML-based meta information about an annotated type (entity, embeddable or mapped superclass).
  *
@@ -64,13 +67,13 @@ public class XmlMetaEntity implements MetaEntity {
 	private final String packageName;
 	private final String defaultPackageName;
 	private final ImportContext importContext;
-	private final List<MetaAttribute> members = new ArrayList<MetaAttribute>();
+	private final List<MetaAttribute> members = new ArrayList<>();
 	private final TypeElement element;
 	private final Context context;
 	private final boolean isMetaComplete;
 
-	private Attributes attributes;
+	private @Nullable Attributes attributes;
-	private EmbeddableAttributes embeddableAttributes;
+	private @Nullable EmbeddableAttributes embeddableAttributes;
 	private AccessTypeInformation accessTypeInfo;
 
 	/**
@@ -90,8 +93,13 @@ public class XmlMetaEntity implements MetaEntity {
 		this( ormEntity.getClazz(), defaultPackageName, element, context, ormEntity.isMetadataComplete() );
 		this.attributes = ormEntity.getAttributes();
 		this.embeddableAttributes = null;
+	}
+
+	static XmlMetaEntity create(Entity ormEntity, String defaultPackageName, TypeElement element, Context context) {
+		XmlMetaEntity entity = new XmlMetaEntity( ormEntity, defaultPackageName, element, context );
 		// entities can be directly initialised
-		init();
+		entity.init();
+		return entity;
 	}
 
 	XmlMetaEntity(MappedSuperclass mappedSuperclass, String defaultPackageName, TypeElement element, Context context) {
@@ -125,15 +133,15 @@ public class XmlMetaEntity implements MetaEntity {
 		this.clazzName = className;
 		this.packageName = pkg;
 		this.context = context;
-		this.importContext = new ImportContextImpl( getPackageName() );
+		this.importContext = new ImportContextImpl( pkg );
 		this.element = element;
-		this.isMetaComplete = initIsMetaComplete( metaComplete );
+		this.isMetaComplete = initIsMetaComplete( context, metaComplete );
 	}
 
 	private final void init() {
 		context.logMessage( Diagnostic.Kind.OTHER, "Initializing type " + getQualifiedName() + "." );
 
-		this.accessTypeInfo = context.getAccessTypeInfo( getQualifiedName() );
+		this.accessTypeInfo = NullnessUtil.castNonNull( context.getAccessTypeInfo( getQualifiedName() ) );
 		if ( attributes != null ) {
 			parseAttributes( attributes );
 		}
@@ -197,11 +205,11 @@ public class XmlMetaEntity implements MetaEntity {
 		return sb.toString();
 	}
 
-	private boolean initIsMetaComplete(Boolean metadataComplete) {
+	private static boolean initIsMetaComplete(Context context, Boolean metadataComplete) {
 		return context.isFullyXmlConfigured() || Boolean.TRUE.equals( metadataComplete );
 	}
 
-	private String[] getCollectionTypes(String propertyName, String explicitTargetEntity, String explicitMapKeyClass, ElementKind expectedElementKind) {
+	private @Nullable String @Nullable[] getCollectionTypes(String propertyName, String explicitTargetEntity, @Nullable String explicitMapKeyClass, ElementKind expectedElementKind) {
 		for ( Element elem : element.getEnclosedElements() ) {
 			if ( !expectedElementKind.equals( elem.getKind() ) ) {
 				continue;
@@ -226,7 +234,7 @@ public class XmlMetaEntity implements MetaEntity {
 		return null;
 	}
 
-	private DeclaredType determineDeclaredType(Element elem) {
+	private @Nullable DeclaredType determineDeclaredType(Element elem) {
 		DeclaredType type = null;
 		if ( elem.asType() instanceof DeclaredType ) {
 			type = ( (DeclaredType) elem.asType() );
@@ -240,17 +248,16 @@ public class XmlMetaEntity implements MetaEntity {
 		return type;
 	}
 
-	private String[] determineTypes(String propertyName, String explicitTargetEntity, String explicitMapKeyClass, DeclaredType type) {
+	private @Nullable String[] determineTypes(String propertyName, String explicitTargetEntity, @Nullable String explicitMapKeyClass, DeclaredType type) {
-		String[] types = new String[3];
+		@Nullable String[] types = new String[3];
 		determineTargetType( type, propertyName, explicitTargetEntity, types );
-		determineCollectionType( type, types );
+		if ( determineCollectionType( type, types ).equals( "jakarta.persistence.metamodel.MapAttribute" ) ) {
-		if ( types[1].equals( "jakarta.persistence.metamodel.MapAttribute" ) ) {
 			determineMapType( type, explicitMapKeyClass, types );
 		}
 		return types;
 	}
 
-	private void determineMapType(DeclaredType type, String explicitMapKeyClass, String[] types) {
+	private void determineMapType(DeclaredType type, @Nullable String explicitMapKeyClass, @Nullable String[] types) {
 		if ( explicitMapKeyClass != null ) {
 			types[2] = explicitMapKeyClass;
 		}
@@ -259,11 +266,11 @@ public class XmlMetaEntity implements MetaEntity {
 		}
 	}
 
-	private void determineCollectionType(DeclaredType type, String[] types) {
+	private String determineCollectionType(DeclaredType type, @Nullable String[] types) {
-		types[1] = COLLECTIONS.get( type.asElement().toString() );
+		return NullnessUtil.castNonNull( types[1] = COLLECTIONS.get( type.asElement().toString() ) );
 	}
 
-	private void determineTargetType(DeclaredType type, String propertyName, String explicitTargetEntity, String[] types) {
+	private void determineTargetType(DeclaredType type, String propertyName, String explicitTargetEntity, @Nullable String[] types) {
 		List<? extends TypeMirror> typeArguments = type.getTypeArguments();
 
 		if ( typeArguments.size() == 0 && explicitTargetEntity == null ) {
@@ -288,7 +295,7 @@ public class XmlMetaEntity implements MetaEntity {
 	 * @return The entity type for this property  or {@code null} if the property with the name and the matching access
 	 *         type does not exist.
 	 */
-	private String getType(String propertyName, String explicitTargetEntity, ElementKind expectedElementKind) {
+	private @Nullable String getType(String propertyName, @Nullable String explicitTargetEntity, ElementKind expectedElementKind) {
 		for ( Element elem : element.getEnclosedElements() ) {
 			if ( !expectedElementKind.equals( elem.getKind() ) ) {
 				continue;
@@ -413,7 +420,7 @@ public class XmlMetaEntity implements MetaEntity {
 		}
 	}
 
-	private void parseEmbeddableAttributes(EmbeddableAttributes attributes) {
+	private void parseEmbeddableAttributes(@Nullable EmbeddableAttributes attributes) {
 		if ( attributes == null ) {
 			return;
 		}
@@ -449,7 +456,7 @@ public class XmlMetaEntity implements MetaEntity {
 	}
 
 	private boolean parseElementCollection(ElementCollection collection) {
-		String[] types;
+		@Nullable String @Nullable[] types;
 		XmlMetaCollection metaCollection;
 		ElementKind elementKind = getElementKind( collection.getAccess() );
 		String explicitTargetClass = determineExplicitTargetEntity( collection.getTargetClass() );
@@ -464,11 +471,14 @@ public class XmlMetaEntity implements MetaEntity {
 			return true;
 		}
 		if ( types != null ) {
-			if ( types[2] == null ) {
+			final String type = NullnessUtil.castNonNull( types[0] );
-				metaCollection = new XmlMetaCollection( this, collection.getName(), types[0], types[1] );
+			final String collectionType = NullnessUtil.castNonNull( types[1] );
+			final String keyType = types[2];
+			if ( keyType == null ) {
+				metaCollection = new XmlMetaCollection( this, collection.getName(), type, collectionType );
 			}
 			else {
-				metaCollection = new XmlMetaMap( this, collection.getName(), types[0], types[1], types[2] );
+				metaCollection = new XmlMetaMap( this, collection.getName(), type, collectionType, keyType );
 			}
 			members.add( metaCollection );
 		}
@@ -495,7 +505,7 @@ public class XmlMetaEntity implements MetaEntity {
 		return explicitTargetClass;
 	}
 
-	private String determineExplicitMapKeyClass(MapKeyClass mapKeyClass) {
+	private @Nullable String determineExplicitMapKeyClass(MapKeyClass mapKeyClass) {
 		String explicitMapKey = null;
 		if ( mapKeyClass != null ) {
 			explicitMapKey = StringUtil.determineFullyQualifiedClassName( defaultPackageName, mapKeyClass.getClazz() );
@@ -504,7 +514,7 @@ public class XmlMetaEntity implements MetaEntity {
 	}
 
 	private boolean parseOneToMany(OneToMany oneToMany) {
-		String[] types;
+		@Nullable String @Nullable [] types;
 		XmlMetaCollection metaCollection;
 		ElementKind elementKind = getElementKind( oneToMany.getAccess() );
 		String explicitTargetClass = determineExplicitTargetEntity( oneToMany.getTargetEntity() );
@@ -517,11 +527,14 @@ public class XmlMetaEntity implements MetaEntity {
 			return true;
 		}
 		if ( types != null ) {
-			if ( types[2] == null ) {
+			final String type = NullnessUtil.castNonNull( types[0] );
-				metaCollection = new XmlMetaCollection( this, oneToMany.getName(), types[0], types[1] );
+			final String collectionType = NullnessUtil.castNonNull( types[1] );
+			final String keyType = types[2];
+			if ( keyType == null ) {
+				metaCollection = new XmlMetaCollection( this, oneToMany.getName(), type, collectionType );
 			}
 			else {
-				metaCollection = new XmlMetaMap( this, oneToMany.getName(), types[0], types[1], types[2] );
+				metaCollection = new XmlMetaMap( this, oneToMany.getName(), type, collectionType, keyType );
 			}
 			members.add( metaCollection );
 		}
@@ -529,7 +542,7 @@ public class XmlMetaEntity implements MetaEntity {
 	}
 
 	private boolean parseManyToMany(ManyToMany manyToMany) {
-		String[] types;
+		@Nullable String @Nullable [] types;
 		XmlMetaCollection metaCollection;
 		ElementKind elementKind = getElementKind( manyToMany.getAccess() );
 		String explicitTargetClass = determineExplicitTargetEntity( manyToMany.getTargetEntity() );
@@ -544,11 +557,14 @@ public class XmlMetaEntity implements MetaEntity {
 			return true;
 		}
 		if ( types != null ) {
-			if ( types[2] == null ) {
+			final String type = NullnessUtil.castNonNull( types[0] );
-				metaCollection = new XmlMetaCollection( this, manyToMany.getName(), types[0], types[1] );
+			final String collectionType = NullnessUtil.castNonNull( types[1] );
+			final String keyType = types[2];
+			if ( keyType == null ) {
+				metaCollection = new XmlMetaCollection( this, manyToMany.getName(), type, collectionType );
 			}
 			else {
-				metaCollection = new XmlMetaMap( this, manyToMany.getName(), types[0], types[1], types[2] );
+				metaCollection = new XmlMetaMap( this, manyToMany.getName(), type, collectionType, keyType );
 			}
 			members.add( metaCollection );
 		}