Message Title

I've added a testcase that demonstrates the problem.
It seems linked to the fact that the fields do not declare an @Type annotation.

It looks like the problem applies to any entity referencing a simple type that is not annotated with @Type and the simple type doesn't declare serializable serialy directly.

java.lang.AssertionError: 'concreteSimpleType' should appear in metamodel class.

Source code for org.hibernate.jpamodelgen.test.usertype.jpa.EntityWithSimpleTypes_.java:
package org.hibernate.jpamodelgen.test.usertype.jpa;

import javax.annotation.Generated;
import javax.persistence.metamodel.SingularAttribute;
import javax.persistence.metamodel.StaticMetamodel;

@Generated(value = "org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor")
@StaticMetamodel(EntityWithSimpleTypes.class)
public abstract class EntityWithSimpleTypes_ {

	public static volatile SingularAttribute<EntityWithSimpleTypes, Integer> integerValue;
	public static volatile SingularAttribute<EntityWithSimpleTypes, Long> id;
	public static volatile SingularAttribute<EntityWithSimpleTypes, ConcreteSerializableSimpleTypeImplementingSerializable> concreteSerializableSimpleTypeImplementingSerializable;

}