bug report: hg backout (without revision)

[Ralf Schmitt]

ralf at red:~/bbot/easyindex/bf$ hg backout
** unknown exception encountered, details follow
** report bug details to http://www.selenic.com/mercurial/bts
** or mercurial at selenic.com
** Mercurial Distributed SCM (version 0.9.4)
Traceback (most recent call last):
   File "/home/ralf/bin/hg", line 5, in <module>
     pkg_resources.run_script('mercurial==0.9.4', 'hg')
   File 
"/home/ralf/pylib2.5/setuptools-0.6c5-py2.5.egg/pkg_resources.py", line 
407, in run_script
     self.require(requires)[0].run_script(script_name, ns)
   File 
"/home/ralf/pylib2.5/setuptools-0.6c5-py2.5.egg/pkg_resources.py", line 
1084, in run_script
     execfile(script_filename, namespace, namespace)
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/EGG-INFO/scripts/hg", 
line 11, in <module>
     mercurial.commands.run()
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/commands.py", 
line 3110, in run
     sys.exit(dispatch(sys.argv[1:], argv0=sys.argv[0]))
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/commands.py", 
line 3107, in dispatch
     return cmdutil.runcatch(u, args, argv0=argv0)
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/cmdutil.py", 
line 37, in runcatch
     return dispatch(ui, args, argv0=argv0)
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/cmdutil.py", 
line 364, in dispatch
     ret = runcommand(ui, options, cmd, d)
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/cmdutil.py", 
line 417, in runcommand
     return checkargs()
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/cmdutil.py", 
line 373, in checkargs
     return cmdfunc()
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/cmdutil.py", 
line 356, in <lambda>
     d = lambda: func(ui, repo, *args, **cmdoptions)
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/commands.py", 
line 176, in backout
     node = repo.lookup(rev)
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/localrepo.py", 
line 363, in lookup
     n = self.changelog._match(key)
   File 
"/home/ralf/pylib2.5/mercurial-0.9.4-py2.5-linux-x86_64.egg/mercurial/revlog.py", 
line 768, in _match
     if len(id) == 20:
TypeError: object of type 'NoneType' has no len()