code: @Override
      public ProtoNetworkDescriptor stage4WriteEquivalentProtoNetwork(
              ProtoNetwork protoNetwork, String protoNetworkRoot) {
          if (protoNetwork == null) {
              throw new InvalidArgument("protoNetwork", protoNetwork);
          }
          if (protoNetworkRoot == null) {
              throw new InvalidArgument("protoNetworkRoot", protoNetworkRoot);
          }
  
          ProtoNetworkDescriptor protoNetworkDescriptor = null;
          try {
              protoNetworkDescriptor = protoNetworkService.write(
                      protoNetworkRoot, protoNetwork);
          } catch (ProtoNetworkError e) {
              error("Could not write out equivalent proto network.");
          }
  
          return protoNetworkDescriptor;
      }
docs: {@inheritDoc}