Plugin fails to starts when using @webhook annotation (The setup method 'add_url_rule' can no longer be called on the application. It has already handled its first request, any changes will not be applied consistently.) #1720

Error: PipelineNotifier failed to activate: PipelineNotifier failed to start : The setup method 'add_url_rule' can no longer be called on the application. It has already handled its first request, any changes will not be applied consistently.

class PipelineNotifier(BotPlugin):
    PIPELINE_STATUS_COMPLETE: str = "complete"
    PIPELINE_STATUS_FAILED: str = "failed"

    @webhook("/pipeline/notify")
    def pipeline_notify(self, request: dict):
        self.log.debug(f"gitlab event: {repr(request)}")
        try:
            event = PipelineNotifierEvent(contributors=request["contributors"],
                                          notify_users=request["notify_users"],
                                          notify_channel=request["notify_channel"],
                                          project=request["project"],
                                          version=request["version"],
                                          release_version=request["release_version"],
                                          job_url=request["job_url"],
                                          pipeline_status=request.get("pipeline_status", ""),
                                          channels_to_notify=request.get("channels_to_notify", []))

            self.handle_pipeline_notifier_event(event)
        except KeyError as e:
            self.log.debug(f"unexpectedly missing key from object. {repr(e)}")

...

... other internal methods used

from errbot import BotPlugin, webhook
from errbot.storage import StoreException


class DevxNotifier(BotPlugin):
    @webhook("/devx/notify")
    def devx_notify(self, request: dict):
        self.log.debug(f"devx notify: {repr(request)}")
        try:
            self.send_card(to=self.build_identifier(request['channel_name']), link=request['link_url'], title=request['title'], color=request['color'], body=request['body'])
        except Exception as e:
            self.log.error(f"Error sending card: {e}")
            return {"status": "error", "message": f"Error sending card: {e}"}

    @property
    def is_slack_backend(self) -> bool:
        self.log.debug(f"Bot mode configured : {self._bot.mode}")
        return self._bot.mode == "slackv3"

    def init_storage(self) -> None:
        """work around storage backend bug

        There is currently a bug in errbot where init_storage is not
        idempotent, but is called multiple times if initialisation fails due to a
        spurious error (e.g. slack API rate limiting).
        We don't use storage, so we will just ignore errors in initialisation
        (which are likely errbot.store.StoreAlreadyOpenError)
        """
        try:
            super().init_storage()
        except StoreException:
            pass

 flask_app.add_url_rule(
                uri_rule, view_func=callable_view, methods=verbs, strict_slashes=False
            )