message: Fix potential nullptr dereferences.
diff: @@ -36,6 +36,9 @@ absl::Status TryDepthwiseConvPlus1x1Conv(
  const std::map<ValueId, TensorDescriptor>& tensor_descriptors,
  std::set<NodeId>* consumed_nodes, GPUOperationsSubgraph* gpu_subgraph) {
  auto* dw_node = graph.GetNode(first_node_id);
  + if (dw_node == nullptr) {
  + return absl::NotFoundError("DepthwiseConvPlus1x1Conv not suitable.");
  + }
  if (OperationTypeFromString(dw_node->operation.type) !=
  OperationType::DEPTHWISE_CONVOLUTION) {
  return absl::NotFoundError("DepthwiseConvPlus1x1Conv not suitable.");
  @@ -50,6 +53,9 @@ absl::Status TryDepthwiseConvPlus1x1Conv(
  return absl::NotFoundError("DepthwiseConvPlus1x1Conv not suitable.");
  }
  auto* conv_node = consumers[0];
  + if (conv_node == nullptr) {
  + return absl::NotFoundError("DepthwiseConvPlus1x1Conv not suitable.");
  + }
  if (consumed_nodes->find(conv_node->id) != consumed_nodes->end()) {
  return absl::NotFoundError("DepthwiseConvPlus1x1Conv not suitable.");
  }
  @@ -94,6 +100,9 @@ absl::Status TryFCFCAdd(
  const std::map<ValueId, TensorDescriptor>& tensor_descriptors,
  std::set<NodeId>* consumed_nodes, GPUOperationsSubgraph* gpu_subgraph) {
  auto* fc0_node = graph.GetNode(first_node_id);
  + if (fc0_node == nullptr) {
  + return absl::NotFoundError("FCFCAdd not suitable.");
  + }
  if (OperationTypeFromString(fc0_node->operation.type) !=
  OperationType::FULLY_CONNECTED) {
  return absl::NotFoundError("FCFCAdd not suitable.");
  @@ -108,6 +117,9 @@ absl::Status TryFCFCAdd(
  return absl::NotFoundError("FCFCAdd not suitable.");
  }
  auto* add_node = consumers[0];
  + if (add_node == nullptr) {
  + return absl::NotFoundError("FCFCAdd not suitable.");
  + }
  if (consumed_nodes->find(add_node->id) != consumed_nodes->end()) {
  return absl::NotFoundError("FCFCAdd not suitable.");
  }
  @@ -120,6 +132,9 @@ absl::Status TryFCFCAdd(
  }
  auto fc1_output_id = add_inputs[0]->id + add_inputs[1]->id - fc0_output_id;
  auto* fc1_node = graph.FindProducer(fc1_output_id);
  + if (fc1_node == nullptr) {
  + return absl::NotFoundError("FCFCAdd not suitable.");
  + }
  if (OperationTypeFromString(fc1_node->operation.type) !=
  OperationType::FULLY_CONNECTED) {
  return absl::NotFoundError("FCFCAdd not suitable.");
  