code: def _get_input(layer, index=0):
      """
      :param layer : NN Layer Proto message
      :param index : Layer input index (Default 0)
      :returns name of input at provided index if present, otherwise None
      """
      if len(layer.input) <= index:
          return None
      return layer.input[index]
  
file_path: turicreate/src/external/coremltools_wrap/coremltools/coremltools/converters/mil/backend/nn/passes/mlmodel_passes.py
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  from itertools import permutations
label_desc: Use image node_id 4 for calling a global function with example usage: _get_input(layer, index) and returns: layer, None