hist/TH1Merger: do not issue a Warning for empty histograms
hist/TH1Merger: do not issue a Warning for empty histograms

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