code: def _get_output(layer, index=0):
      """
      :param layer : NN Layer Proto message
      :param index : Layer output index (Default 0)
      :returns name of output at provided index if present, otherwise None
      """
      if len(layer.output) <= index:
          return None
      return layer.output[index]
  
file_path: coremltools/coremltools/converters/mil/backend/nn/passes/mlmodel_passes.py
label_desc: Use image node_id 5 for calling a global function with example usage: _get_output(layer, index) and returns: layer, None