code: def _get_config_type(cla55: type) -> Optional[str]:
      
      # Special handling for pytorch RNN types:
      if cla55 == torch.nn.RNN:
          return "rnn"
      elif cla55 == torch.nn.LSTM:
          return "lstm"
      elif cla55 == torch.nn.GRU:
          return "gru"
  
      for subclass_dict in Registrable._registry.values():
          for name, subclass in subclass_dict.items():
              if subclass == cla55:
                  return name
  
          # Special handling for initializer functions
              if hasattr(subclass, '_initializer_wrapper'):
                  sif = subclass()._init_function
                  if sif == cla55:
                      return sif.__name__.rstrip("_")
  
      return None
docs: Find the name (if any) that a subclass was registered under.
      We do this simply by iterating through the registry until we
      find it.