--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -73,7 +73,7 @@ class revlog:
if id in hex(n):
c.append(n)
if len(c) > 1: raise KeyError("Ambiguous identifier")
- if len(c) < 1: raise KeyError
+ if len(c) < 1: raise KeyError("No match found")
return c[0]
return None