code: def _maybe_warn_for_unseparable_batches(self, output_key: str):
          
          if  output_key not in self._warn_for_unseparable_batches:
              logger.warning(f"Encountered the {output_key} key in the model's return dictionary which "
                             "couldn't be split by the batch size. Key will be ignored.")
              # We only want to warn once for this key,
              # so we set this to false so we don't warn again.
              self._warn_for_unseparable_batches.add(output_key)
docs: This method warns once if a user implements a model which returns a dictionary with
          values which we are unable to split back up into elements of the batch. This is controlled
          by a class attribute ``_warn_for_unseperable_batches`` because it would be extremely verbose
          otherwise.