message: add default_output_alternative_key argument for make_custom_export_strategy, as required by multi-head.
diff: @@ -42,7 +42,8 @@ def make_custom_export_strategy(name,
  feature_columns,
  export_input_fn,
  use_core_columns=False,
  - feature_engineering_fn=None):
  + feature_engineering_fn=None,
  + default_output_alternative_key=None):
  """Makes custom exporter of GTFlow tree format.
  Args:
  @@ -54,12 +55,17 @@ def make_custom_export_strategy(name,
  `InputFnOps`.
  use_core_columns: A boolean, whether core feature columns were used.
  feature_engineering_fn: Feature eng function to be called on the input.
  + default_output_alternative_key: the name of the head to serve when an
  + incoming serving request does not explicitly request a specific head.
  + Not needed for single-headed models.
  Returns:
  An `ExportStrategy`.
  """
  base_strategy = saved_model_export_utils.make_export_strategy(
  - serving_input_fn=export_input_fn, strip_default_attrs=True)
  + serving_input_fn=export_input_fn,
  + strip_default_attrs=True,
  + default_output_alternative_key=default_output_alternative_key)
  input_fn = export_input_fn()
  features = input_fn.features
  if feature_engineering_fn is not None:
  