HHH-18675: Fix for testcase. If property is 'synthetic' then create no attribute for the jpa model.

(cherry picked from commit bc4804a)

Author: leonschenk

hibernate-core/src/main/java/org/hibernate/mapping/Property.java

@@ -496,7 +496,7 @@ public Generator createGenerator(RuntimeModelCreationContext context) {
 	}
 
 	public Property copy() {
-		final Property property = new Property();
+		final Property property = this instanceof SyntheticProperty ? new SyntheticProperty() : new Property();
 		property.setName( getName() );
 		property.setValue( getValue() );
 		property.setCascade( getCascade() );

hibernate-core/src/main/java/org/hibernate/metamodel/internal/MetadataContext.java

@@ -279,8 +279,10 @@ public Map<String, IdentifiableDomainType<?>> getIdentifiableTypesByName() {
 			attribute = factoryFunction.apply( entityType, genericProperty );
 			if ( !property.isGeneric() ) {
 				final PersistentAttribute<X, ?> concreteAttribute = factoryFunction.apply( entityType, property );
-				//noinspection unchecked
-				( (AttributeContainer<X>) entityType ).getInFlightAccess().addConcreteGenericAttribute( concreteAttribute );
+				if ( concreteAttribute != null ) {
+					@SuppressWarnings("unchecked") final AttributeContainer<X> attributeContainer = (AttributeContainer<X>) entityType;
+					attributeContainer.getInFlightAccess().addConcreteGenericAttribute( concreteAttribute );
+				}
 			}
 		}
 		else {