Running

// repro.C
void repro() {
  TMVA::Experimental::RBDT<> bdt("Bc2TauNu_BDT", "doesnotexist.root");
}

as

root -l -b -q repro.C

yields:

Error in <TFile::TFile>: file /tmp/doesnotexist.root does not exist

 *** Break *** segmentation violation

RBDT should probably protect nullptr accesses or similar and throw an exception or return an error rather than crashing.