Add a warning message when the RooAddPdf normalization set is a nullptr
Add a warning message when the RooAddPdf normalization set is a nullptr

root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,olifre/root,olifre/root