Fill in default values for grad_ys. Args: grad_ys: List of gradients, can contain None. ys: List of tensors. colocate_gradients_with_ops: If True, try colocating gradients with the corresponding op. Returns: A list of gradients to use, without None. Raises: ValueEr
(grad_ys, ys, colocate_gradients_with_ops)
source not stored for this graph (policy: none)