HHH-8914 double negation broken on JPA criteria

hibernate-entitymanager/src/main/java/org/hibernate/jpa/criteria/predicate/AbstractPredicateImpl.java

@@ -40,14 +40,13 @@ import org.hibernate.jpa.criteria.expression.ExpressionImpl;
 public abstract class AbstractPredicateImpl
 		extends ExpressionImpl<Boolean>
 		implements PredicateImplementor, Serializable {
-	private boolean negated;
 
 	protected AbstractPredicateImpl(CriteriaBuilderImpl criteriaBuilder) {
 		super( criteriaBuilder, Boolean.class );
 	}
 
 	public boolean isNegated() {
-		return negated;
+		return false;
 	}
 
 	public Predicate not() {

hibernate-entitymanager/src/main/java/org/hibernate/jpa/criteria/predicate/NegatedPredicateWrapper.java

@@ -107,19 +107,19 @@ public class NegatedPredicateWrapper extends ExpressionImpl<Boolean> implements
 
 	@Override
 	public String render(boolean isNegated, RenderingContext renderingContext) {
-		return render( renderingContext );
-	}
-
-	@Override
-	public String render(RenderingContext renderingContext) {
 		if ( isJunction() ) {
 			return CompoundPredicate.render( this, renderingContext );
 		}
 		else {
-			return predicate.render( isNegated(), renderingContext );
+			return predicate.render( isNegated, renderingContext );
 		}
 	}
 
+	@Override
+	public String render(RenderingContext renderingContext) {
+		return render( isNegated(), renderingContext );
+	}
+
 	@Override
 	public String renderProjection(RenderingContext renderingContext) {
 		return render( renderingContext );

hibernate-entitymanager/src/test/java/org/hibernate/jpa/test/criteria/basic/BasicCriteriaUsageTest.java

@@ -126,4 +126,59 @@ public class BasicCriteriaUsageTest extends BaseEntityManagerFunctionalTestCase
 		em.getTransaction().commit();
 		em.close();
 	}
+    
+	@Test
+	@TestForIssue( jiraKey = "HHH-8914" )
+	public void testDoubleNegation() {
+		Wall wall1 = new Wall();
+		wall1.setColor( "yellow" );
+		Wall wall2 = new Wall();
+		wall2.setColor( null );
+		
+		EntityManager em = getOrCreateEntityManager();
+		em.getTransaction().begin();
+		em.persist( wall1 );
+		em.persist( wall2 );
+		em.getTransaction().commit();
+		em.clear();
+		
+		em.getTransaction().begin();
+		
+		// Although the examples are simplified and the usages appear pointless,
+		// double negatives can occur in some dynamic applications (regardless
+		// if it results from bad design or not).  Ensure we handle them as expected.
+		
+		CriteriaBuilder cb = em.getCriteriaBuilder();
+		CriteriaQuery<Wall> query = cb.createQuery( Wall.class );
+		Root<Wall> root = query.from( Wall.class );
+		query.select( root ).where(
+				cb.not(
+						cb.isNotNull( root.get( "color" ) ) ) );
+		Wall result = em.createQuery( query ).getSingleResult();
+		assertNotNull( result );
+		assertEquals( null, result.getColor() );
+		
+		query = cb.createQuery( Wall.class );
+		root = query.from( Wall.class );
+		query.select( root ).where(
+				cb.not(
+						cb.not(
+								cb.isNull( root.get( "color" ) ) ) ) );
+		result = em.createQuery( query ).getSingleResult();
+		assertNotNull( result );
+		assertEquals( null, result.getColor() );
+		
+		query = cb.createQuery( Wall.class );
+		root = query.from( Wall.class );
+		query.select( root ).where(
+				cb.not(
+						cb.not(
+								cb.isNotNull( root.get( "color" ) ) ) ) );
+		result = em.createQuery( query ).getSingleResult();
+		assertNotNull( result );
+		assertEquals( "yellow", result.getColor() );
+		
+		em.getTransaction().commit();
+		em.close();
+	}
 }