Fix filterNotNull and mapNotNull for streams.

libraries/tools/kotlin-stdlib-gen/src/templates/Filtering.kt

@@ -305,7 +305,7 @@ fun filtering(): List<GenericFunction> {
         returns(Streams) { "Stream<T>" }
         body(Streams) {
             """
-            return FilteringStream(this, false, { it != null }) as Stream<T>
+            return FilteringStream(this, false, { it == null }) as Stream<T>
             """
         }
     }

libraries/tools/kotlin-stdlib-gen/src/templates/Mapping.kt

@@ -63,7 +63,7 @@ fun mapping(): List<GenericFunction> {
         inline(false, Streams)
         body(Streams) {
             """
-            return TransformingStream(FilteringStream(this, false, { it != null }) as Stream<T>, transform)
+            return TransformingStream(FilteringStream(this, false, { it == null }) as Stream<T>, transform)
             """
         }
     }