HHH-16564 allow null in 'select new' argument list

hibernate-core/src/main/java/org/hibernate/query/sqm/sql/BaseSqmToSqlAstConverter.java

@@ -391,10 +391,13 @@
 import org.hibernate.type.BasicType;
 import org.hibernate.type.JavaObjectType;
 import org.hibernate.type.SqlTypes;
+import org.hibernate.type.descriptor.WrapperOptions;
 import org.hibernate.type.descriptor.converter.spi.BasicValueConverter;
+import org.hibernate.type.descriptor.java.AbstractClassJavaType;
 import org.hibernate.type.descriptor.java.JavaType;
 import org.hibernate.type.descriptor.java.JavaTypeHelper;
 import org.hibernate.type.descriptor.jdbc.JdbcTypeIndicators;
+import org.hibernate.type.descriptor.jdbc.NullJdbcType;
 import org.hibernate.type.internal.BasicTypeImpl;
 import org.hibernate.type.spi.TypeConfiguration;
 import org.hibernate.usertype.UserVersionType;
@@ -4872,8 +4875,17 @@ public Expression visitLiteral(SqmLiteral<?> literal) {
 			}
 			final MappingModelExpressible<?> keyExpressible = getKeyExpressible( mappingModelExpressible );
 			if ( keyExpressible == null ) {
-				// Default to the Object type
+				// treat Void as the bottom type, the class of null
-				return new QueryLiteral<>( null, basicType( Object.class ) );
+				return new QueryLiteral<>( null, new JavaObjectType(NullJdbcType.INSTANCE, new AbstractClassJavaType<>(Void.class) {
+					@Override
+					public <X> X unwrap(Object value, Class<X> type, WrapperOptions options) {
+						return null;
+					}
+					@Override
+					public <X> Void wrap(X value, WrapperOptions options) {
+						return null;
+					}
+				} ) );
 			}
 
 			final List<Expression> expressions = new ArrayList<>( keyExpressible.getJdbcTypeCount() );

hibernate-core/src/main/java/org/hibernate/query/sqm/tree/expression/Compatibility.java

@@ -57,6 +57,11 @@ public static boolean areAssignmentCompatible(Class to, Class from) {
 		assert to != null;
 		assert from != null;
 
+		if ( from == Void.class ) {
+			// treat Void as the bottom type, the class of null
+			return true;
+		}
+
 		if ( to.isAssignableFrom( from ) ) {
 			return true;
 		}

hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/CastNullSelectExpressionTest.java

@@ -61,6 +61,36 @@ public void testSelectNewCastNull(SessionFactoryScope scope) {
 		);
 	}
 
+	@Test
+	@TestForIssue(jiraKey = "HHH-16564")
+	public void testSelectNewNull(SessionFactoryScope scope) {
+		scope.inTransaction(
+				(session) -> {
+					Person result = (Person) session.createQuery(
+							"select new Person( id, firstName, null, lastName ) from Person where lastName='Munster'"
+					).uniqueResult();
+					assertEquals( "Herman", result.firstName );
+					assertNull( result.middleName );
+					assertEquals( "Munster", result.lastName );
+				}
+		);
+	}
+
+	@Test
+	@TestForIssue(jiraKey = "HHH-16564")
+	public void testSelectNull(SessionFactoryScope scope) {
+		scope.inTransaction(
+				(session) -> {
+					Object[] result = (Object[]) session.createQuery(
+							"select id, firstName, null, lastName from Person where lastName='Munster'"
+					).uniqueResult();
+					assertEquals( "Herman", result[1] );
+					assertNull( result[2] );
+					assertEquals( "Munster", result[3] );
+				}
+		);
+	}
+
 	@BeforeEach
 	public void createTestData(SessionFactoryScope scope) {
 		scope.inTransaction(