code: def create(self, *args, **kwargs):
          
          if self.activity_type != ActivityType.SUBPROCESS:
              raise IllegalArgumentError("One can only create a task under a subprocess.")
          return self._client.create_activity(self.id, *args, **kwargs)
docs: Create a new activity belonging to this subprocess.
  
          See :func:`pykechain.Client.create_activity` for available parameters.
  
          :raises IllegalArgumentError: if the `Activity` is not a `SUBPROCESS`.
          :raises APIError: if an Error occurs.