Backport Specification.unrestricted() to 3.5.x.

Introducing a replacement method for the deprecated `where(…)` method.

Closes #3942

Author: mp911de

spring-data-jpa/src/main/java/org/springframework/data/jpa/domain/Specification.java

@@ -64,6 +64,17 @@ static <T> Specification<T> not(@Nullable Specification<T> spec) {
 				};
 	}
 
+	/**
+	 * Simple static factory method to create a specification matching all objects.
+	 *
+	 * @param <T> the type of the {@link Root} the resulting {@literal Specification} operates on.
+	 * @return guaranteed to be not {@literal null}.
+	 * @since 3.5.2
+	 */
+	static <T> Specification<T> unrestricted() {
+		return (root, query, builder) -> null;
+	}
+
 	/**
 	 * Simple static factory method to add some syntactic sugar around a {@link Specification}.
 	 *
@@ -72,11 +83,12 @@ static <T> Specification<T> not(@Nullable Specification<T> spec) {
 	 * @param spec can be {@literal null}.
 	 * @return guaranteed to be not {@literal null}.
 	 * @since 2.0
-	 * @deprecated since 3.5, to be removed with 4.0 as we no longer want to support {@literal null} specifications.
+	 * @deprecated since 3.5, to be removed with 4.0 as we no longer want to support {@literal null} specifications. Use
+	 *             {@link #unrestricted()} instead.
 	 */
 	@Deprecated(since = "3.5.0", forRemoval = true)
 	static <T> Specification<T> where(@Nullable Specification<T> spec) {
-		return spec == null ? (root, query, builder) -> null : spec;
+		return spec == null ? unrestricted() : spec;
 	}
 
 	/**