HHH-18979 add Restriction.none() as useful degenerate case

Author: gavinking

hibernate-core/src/main/java/org/hibernate/query/Restriction.java

@@ -130,4 +130,27 @@ static <T> Restriction<T> and(Restriction<T>... restrictions) {
 	static <T> Restriction<T> or(Restriction<T>... restrictions) {
 		return new Disjunction<>( java.util.List.of( restrictions ) );
 	}
+
+	static <T> Restriction<T> none() {
+		return new Restriction<>() {
+			final Restriction<T> none = this;
+			@Override
+			public Restriction<T> negated() {
+				return new Restriction<>() {
+					@Override
+					public Predicate toPredicate(Root<? extends T> root, CriteriaBuilder builder) {
+						return builder.disjunction();
+					}
+					@Override
+					public Restriction<T> negated() {
+						return none;
+					}
+				};
+			}
+			@Override
+			public Predicate toPredicate(Root<? extends T> root, CriteriaBuilder builder) {
+				return builder.conjunction();
+			}
+		};
+	}
 }

hibernate-core/src/test/java/org/hibernate/orm/test/query/restriction/RestrictionTest.java

@@ -81,6 +81,16 @@ void test(SessionFactoryScope scope) {
 								Range.singleCaseInsensitiveValue("hibernate in action") ) )
 						.getSingleResultOrNull() );
 		assertEquals( "9781932394153", bookByTitleUnsafe.isbn );
+		List<Book> allBooks = scope.fromSession( session ->
+				session.createSelectionQuery( "from Book", Book.class)
+						.addRestriction( Restriction.none() )
+						.getResultList() );
+		assertEquals( 2, allBooks.size() );
+		List<Book> noBooks = scope.fromSession( session ->
+				session.createSelectionQuery( "from Book", Book.class)
+						.addRestriction( Restriction.none().negated() )
+						.getResultList() );
+		assertEquals( 0, noBooks.size() );
 	}
 
 	@Entity(name="Book")