message: Modify to return an error specifying an axis argument must be given instead of an error due to being unable to convert a null tensor.
diff: @@ -120,7 +120,7 @@ def expand_dims(input, axis=None, name=None, dim=None):
  axis: 0-D (scalar). Specifies the dimension index at which to
  expand the shape of `input`. Must be in the range
  `[-rank(input) - 1, rank(input)]`.
  - name: The name of the output `Tensor`.
  + name: The name of the output `Tensor` (optional).
  dim: 0-D (scalar). Equivalent to `axis`, to be deprecated.
  Returns:
  @@ -128,9 +128,11 @@ def expand_dims(input, axis=None, name=None, dim=None):
  dimension of size 1 added.
  Raises:
  - ValueError: if both `dim` and `axis` are specified.
  + ValueError: if either both or neither of `dim` and `axis` are specified.
  """
  axis = deprecation.deprecated_argument_lookup("axis", axis, "dim", dim)
  + if axis is None:
  + raise ValueError("Must specify an axis argument to tf.expand_dims()")
  return gen_array_ops.expand_dims(input, axis, name)
  