Unfortunately I receive this error message when I run my macro:
Error in <TTreeReaderValueBase::GetBranchDataType()>: Unknown type and class combination: -1, string
Error in <TTreeReaderValueBase::CreateProxy()>: The branch FileName contains data of type {UNDETERMINED TYPE}, which does not have a dictionary.
It seems to be a problem specific to TTreeReaderValue. Because when I read a different branch containing a std::vector<std::string> it works without problems:
I just built the master branch and I can confirm that the problem is fixed. If it is not too much work, it would be nice for us if this fix would be available within the next patch.