--- a/mercurial/branchmap.py	Sat Mar 02 13:28:17 2019 -0800
+++ b/mercurial/branchmap.py	Sat Mar 02 05:24:35 2019 +0530
@@ -360,7 +360,7 @@
 
         duration = util.timer() - starttime
         repo.ui.log('branchcache', 'updated %s branch cache in %.4f seconds\n',
-                    repo.filtername, duration)
+                    repo.filtername or b'None', duration)
 
         self.write(repo)