debugcommands: use repo[None].walk instead of repo.walk

mercurial/debugcommands.py

@@ -2168,7 +2168,7 b' def debugupgraderepo(ui, repo, run=False'
 def debugwalk(ui, repo, *pats, **opts):
     """show how files match on given patterns"""
     m = scmutil.match(repo[None], pats, opts)
-    items = list(repo.walk(m))
+    items = list(repo[None].walk(m))
     if not items:
         return
     f = lambda fn: fn