diff -r 8ca92bcb3083 -r 7eb701e355bd mercurial/localrepo.py
--- a/mercurial/localrepo.py	Thu Nov 21 15:46:35 2019 -0500
+++ b/mercurial/localrepo.py	Fri Nov 22 21:42:04 2019 +0900
@@ -1568,7 +1568,7 @@
             else:
                 raise error.ProgrammingError(
                     b"unsupported changeid '%s' of type %s"
-                    % (changeid, pycompat.sysstr(type(changeid)))
+                    % (changeid, pycompat.bytestr(type(changeid)))
                 )
 
             return context.changectx(self, rev, node)
@@ -2086,11 +2086,10 @@
             tracktags(tr2)
             repo = reporef()
 
-            r = repo.ui.configsuboptions(
-                b'experimental', b'single-head-per-branch'
-            )
-            singlehead, singleheadsub = r
+            singleheadopt = (b'experimental', b'single-head-per-branch')
+            singlehead = repo.ui.configbool(*singleheadopt)
             if singlehead:
+                singleheadsub = repo.ui.configsuboptions(*singleheadopt)[1]
                 accountclosed = singleheadsub.get(
                     b"account-closed-heads", False
                 )