diff -r 4ccd5ec565c2 -r d5ccc059fbcd mercurial/debugcommands.py
--- a/mercurial/debugcommands.py	Wed Jul 22 00:09:17 2020 -0700
+++ b/mercurial/debugcommands.py	Fri Jul 24 11:24:59 2020 -0700
@@ -1669,7 +1669,7 @@
 
     # templates
     p = templater.templatedir()
-    fm.write(b'templatedirs', b'checking templates (%s)...\n', p)
+    fm.write(b'templatedirs', b'checking templates (%s)...\n', p or b'')
     fm.condwrite(not p, b'', _(b" no template directories found\n"))
     if p:
         m = templater.templatepath(b"map-cmdline.default")