diff --git a/mercurial/utils/stringutil.py b/mercurial/utils/stringutil.py
--- a/mercurial/utils/stringutil.py
+++ b/mercurial/utils/stringutil.py
@@ -29,6 +29,8 @@
         if bprefix:
             return "b'%s'" % escapestr(o)
         return "'%s'" % escapestr(o)
+    elif o is None:
+        return 'None'
     elif isinstance(o, bytearray):
         # codecs.escape_encode() can't handle bytearray, so escapestr fails
         # without coercion.