code: def _has_custom_layer(spec):
      """
  
      Returns true if the given protobuf specification has a custom layer, and false otherwise.
  
      Parameters
      ----------
      spec: mlmodel spec
  
      Returns
      -------
  
      True if the protobuf specification contains a neural network with a custom layer, False otherwise.
  
      """
  
      layers = _get_nn_layers(spec)
      for layer in layers:
          if layer.WhichOneof("layer") == "custom":
              return True
  
      return False
  
imports: import math
  import numpy
  import os
  import six
  import warnings
  import sys
  from coremltools.proto import Model_pb2
  from coremltools.models._deprecation import deprecated
  from .._deps import _HAS_SKLEARN
label_desc: Use image node_id 20 for calling a global function with example usage: _has_custom_layer(spec) and returns: False, True