message: Quick fix in TFLite writer lib related to optional tensors.
diff: @@ -320,6 +320,14 @@ TfLiteStatus SubgraphWriter::CheckInputOutput(
  subgraph_->node_and_registration(op_index);
  const TfLiteNode& node = node_and_registration->first;
  for (int tensor_index : TfLiteIntArrayView(node.inputs)) {
  + if (tensor_index < 0) {
  + // Skip if optional input not present.
  + if (tensor_index == kTfLiteOptionalTensor) {
  + continue;
  + } else {
  + return kTfLiteError;
  + }
  + }
  if (TfLiteTensor* tensor = subgraph_->tensor(tensor_index)) {
  // Skip constant tensors.
  if (tensor->allocation_type == kTfLiteMmapRo) {
  