message: Do not assert for null device memory pointer if size is zero.
diff: @@ -588,7 +588,8 @@ xla::StatusOr<xla::ShapedBuffer> XRTTupleAllocation::ToShapedBuffer() {
  allocator_->platform(), device_ordinal_);
  for (const auto& index_buffer : buffers_) {
  if (index_buffer.second == nullptr ||
  - index_buffer.second->allocation().is_null()) {
  + (index_buffer.second->allocation().is_null() &&
  + index_buffer.second->allocation().size() > 0)) {
  return errors::InvalidArgument("Literal buffer at index ",
  index_buffer.first.ToString(),
  " has been released");
  @@ -652,7 +653,8 @@ xla::StatusOr<xla::ExecutionInput> XRTTupleAllocation::ToExecutionInput(
  xla::ExecutionInput result(on_device_shape());
  for (const auto& index_buffer : buffers_) {
  if (index_buffer.second == nullptr ||
  - index_buffer.second->allocation().is_null()) {
  + (index_buffer.second->allocation().is_null() &&
  + index_buffer.second->allocation().size() > 0)) {
  return errors::InvalidArgument("Literal buffer at index ",
  index_buffer.first.ToString(),
  " has been released");
  