code: def _find_unique_encoder_key(self, key):
      assert key in self.encoders, f"MMFT doesn't have {key} encoder."
      for modality in self.config.modalities:
          if modality.key == key:
              assert (
                  len(
                      [
                          m
                          for m in self.config.modalities
                          if m.key == modality.key
                      ]
                  )
                  == 1
              ), f"MMFT has multiple modalities with the same key {key}."
              assert (
                  len(
                      [
                          m
                          for m in self.config.modalities
                          if m.type == modality.type
                      ]
                  )
                  == 1
              ), f"Encoder {key} should be the only encoder for {modality.type}."
              return key
  
imports: import logging
  from dataclasses import dataclass, field
  from typing import Dict, List, Optional
  import torch
  from mmf.common.registry import registry
  from mmf.models.transformers.base import BaseTransformer, BaseTransformerBackendConfig, BaseTransformerHead, BaseTransformerModalityConfig
  from mmf.models.transformers.heads.mlp import MLP
  from mmf.modules.encoders import ResNet152ImageEncoder
  from mmf.utils.build import build_encoder
  from omegaconf import MISSING, OmegaConf
  from torch import nn, Tensor
label_desc: Use image node_id 16 for calling the MMFTransformer obj's underlying member method code with example usage: obj._find_unique_encoder_key(key) and returns: key