introduced workaround for proto_utils
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index a285310..bb4058f 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -858,6 +858,7 @@
src/cpp/common/channel_arguments.cc \
src/cpp/common/completion_queue.cc \
src/cpp/common/rpc_method.cc \
+src/cpp/proto/proto_serializer.cc \
src/cpp/proto/proto_utils.cc \
src/cpp/server/async_generic_service.cc \
src/cpp/server/create_default_thread_pool.cc \