[COMPONENT][Posting] Fix request handling issues that resulted from splitting creation and controller

components/Posting/Controller/Posting.php

@@ -53,7 +53,7 @@ class Posting extends Controller
                         locale: $data['language'],
                         scope: VisibilityScope::from($data['visibility']),
                         targets: isset($target) ? [$target] : [],
-                        reply_to: $data['reply_to_id'],
+                        reply_to: \array_key_exists('reply_to_id', $data) ? $data['reply_to_id'] : null,
                         attachments: $data['attachments'],
                         process_note_content_extra_args: $extra_args,
                     );