$ hg backout ** unknown exception encountered, details follow ** report bug details to http://www.selenic.com/mercurial/bts ** or mercurial@selenic.com ** Mercurial Distributed SCM (version 0.9.4) Traceback (most recent call last): File "/usr/bin/hg", line 11, in mercurial.commands.run() File "/usr/lib64/python2.5/site-packages/mercurial/commands.py", line 3110, in run sys.exit(dispatch(sys.argv[1:], argv0=sys.argv[0])) File "/usr/lib64/python2.5/site-packages/mercurial/commands.py", line 3107, in dispatch return cmdutil.runcatch(u, args, argv0=argv0) File "/usr/lib64/python2.5/site-packages/mercurial/cmdutil.py", line 37, in runcatch return dispatch(ui, args, argv0=argv0) File "/usr/lib64/python2.5/site-packages/mercurial/cmdutil.py", line 364, in dispatch ret = runcommand(ui, options, cmd, d) File "/usr/lib64/python2.5/site-packages/mercurial/cmdutil.py", line 417, in runcommand return checkargs() File "/usr/lib64/python2.5/site-packages/mercurial/cmdutil.py", line 373, in checkargs return cmdfunc() File "/usr/lib64/python2.5/site-packages/mercurial/cmdutil.py", line 356, in d = lambda: func(ui, repo, *args, **cmdoptions) File "/usr/lib64/python2.5/site-packages/mercurial/commands.py", line 176, in backout node = repo.lookup(rev) File "/usr/lib64/python2.5/site-packages/mercurial/localrepo.py", line 363, in lookup n = self.changelog._match(key) File "/usr/lib64/python2.5/site-packages/mercurial/revlog.py", line 768, in _match if len(id) == 20: TypeError: object of type 'NoneType' has no len()