message: Skip optional tensors for float16 quantization.
diff: @@ -482,6 +482,10 @@ TfLiteStatus QuantizeWeightsFloat16(flatbuffers::FlatBufferBuilder* builder,
  for (int i = 0; i < subgraph->operators.size(); ++i) {
  OperatorT* op = subgraph->operators[i].get();
  for (auto tensor_idx : op->inputs) {
  + // Skip optional tensors.
  + if (tensor_idx == kTfLiteOptionalTensor) {
  + continue;
  + }
  TensorT* tensor = subgraph->tensors[tensor_idx].get();
  BufferT* buffer = model->buffers[tensor->buffer].get();
  if (buffer == nullptr) {
  