HHH-15278 NPE when NULL is used in the projection

hibernate-core/src/main/java/org/hibernate/sql/ast/spi/AbstractSqlAstTranslator.java

@@ -173,9 +173,12 @@ import org.hibernate.sql.exec.spi.JdbcUpdate;
 import org.hibernate.sql.results.internal.SqlSelectionImpl;
 import org.hibernate.sql.results.jdbc.internal.JdbcValuesMappingProducerStandard;
 import org.hibernate.type.BasicType;
+import org.hibernate.type.SqlTypes;
 import org.hibernate.type.StandardBasicTypes;
 import org.hibernate.type.descriptor.WrapperOptions;
 import org.hibernate.type.descriptor.jdbc.JdbcLiteralFormatter;
+import org.hibernate.type.descriptor.sql.DdlType;
+import org.hibernate.type.descriptor.sql.spi.DdlTypeRegistry;
 
 import static org.hibernate.query.sqm.TemporalUnit.NANOSECOND;
 import static org.hibernate.sql.ast.SqlTreePrinter.logSqlAst;
@@ -4293,15 +4296,22 @@ public abstract class AbstractSqlAstTranslator<T extends JdbcOperation> implemen
 		}
 		else {
 			final SqlExpressible expressionType = (SqlExpressible) castTarget.getExpressionType();
+			final DdlTypeRegistry ddlTypeRegistry = getSessionFactory().getTypeConfiguration().getDdlTypeRegistry();
+			DdlType ddlType = ddlTypeRegistry
+					.getDescriptor( expressionType.getJdbcMapping().getJdbcType().getDefaultSqlTypeCode() );
+			if ( ddlType == null ) {
+				// this may happen when selecting a null value like `SELECT null from ...`
+				// some dbs need the value to be cast so not knowing the real type we fall back to INTEGER
+				ddlType = ddlTypeRegistry.getDescriptor( SqlTypes.INTEGER );
+			}
+
 			appendSql(
-					sessionFactory.getTypeConfiguration().getDdlTypeRegistry()
-							.getDescriptor( expressionType.getJdbcMapping().getJdbcType().getDefaultSqlTypeCode() )
-							.getCastTypeName(
-									expressionType,
-									castTarget.getLength(),
-									castTarget.getPrecision(),
-									castTarget.getScale()
-							)
+					ddlType.getCastTypeName(
+							expressionType,
+							castTarget.getLength(),
+							castTarget.getPrecision(),
+							castTarget.getScale()
+					)
 			);
 		}
 	}

hibernate-core/src/main/java/org/hibernate/type/NullType.java

@@ -32,4 +32,9 @@ public class NullType extends JavaObjectType {
 	public String getName() {
 		return "null";
 	}
+
+	@Override
+	protected boolean registerUnderJavaType() {
+		return false;
+	}
 }

hibernate-core/src/main/java/org/hibernate/type/descriptor/jdbc/NullJdbcType.java

@@ -8,6 +8,7 @@ package org.hibernate.type.descriptor.jdbc;
 
 import java.sql.CallableStatement;
 import java.sql.PreparedStatement;
+import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Types;
 
@@ -34,7 +35,23 @@ public class NullJdbcType implements JdbcType {
 
 	@Override
 	public <X> ValueExtractor<X> getExtractor(JavaType<X> javaType) {
-		return null;
+		return new BasicExtractor<X>(javaType, this ) {
+			@Override
+			protected X doExtract(ResultSet rs, int paramIndex, WrapperOptions options) throws SQLException {
+				return null;
+			}
+
+			@Override
+			protected X doExtract(CallableStatement statement, int index, WrapperOptions options) throws SQLException {
+				return null;
+			}
+
+			@Override
+			protected X doExtract(CallableStatement statement, String name, WrapperOptions options)
+					throws SQLException {
+				return null;
+			}
+		};
 	}
 
 	@Override