message: Registers None gradients for ArgMax
diff: @@ -35,6 +35,12 @@ def _safe_shape_div(x, y):
  return x // math_ops.maximum(y, 1)
  +@ops.RegisterGradient("ArgMax")
  +def _ArgMaxGrad(op, grad):
  + del op, grad
  + return [None, None]
  +
  +
  @ops.RegisterGradient("Sum")
  def _SumGrad(op, grad):
  """Gradient for Sum."""
  