adding a commit message to a changeset which is hg histedit fold'ed

** Python 2.6.2 (r262:71600, Jun  4 2010, 18:28:58) [GCC 4.4.3 20100127 (Red Hat 4.4.3-4)]
** Mercurial Distributed SCM (version 2.1.1)
** Extensions loaded: graphlog, extdiff, transplant, rebase, churn, convert, mq, contains, activity, reviewboard, hgshelve, buginfo, histedit
Traceback (most recent call last):
  File "/usr/bin/hg", line 38, in <module>
    mercurial.dispatch.run()
  File "/usr/lib64/python2.6/site-packages/mercurial/dispatch.py", line 27, in run
    sys.exit((dispatch(request(sys.argv[1:])) or 0) & 255)
  File "/usr/lib64/python2.6/site-packages/mercurial/dispatch.py", line 64, in dispatch
    return _runcatch(req)
  File "/usr/lib64/python2.6/site-packages/mercurial/dispatch.py", line 87, in _runcatch
    return _dispatch(req)
  File "/usr/lib64/python2.6/site-packages/mercurial/dispatch.py", line 683, in _dispatch
    cmdpats, cmdoptions)
  File "/usr/lib64/python2.6/site-packages/mercurial/dispatch.py", line 465, in runcommand
    ret = _runcommand(ui, options, cmd, d)
  File "/usr/lib64/python2.6/site-packages/mercurial/dispatch.py", line 737, in _runcommand
    return checkargs()
  File "/usr/lib64/python2.6/site-packages/mercurial/dispatch.py", line 691, in checkargs
    return cmdfunc()
  File "/usr/lib64/python2.6/site-packages/mercurial/dispatch.py", line 680, in <lambda>
    d = lambda: util.checksignature(func)(ui, *args, **cmdoptions)
  File "/usr/lib64/python2.6/site-packages/mercurial/util.py", line 456, in check
    return func(*args, **kwargs)
  File "/usr/lib64/python2.6/site-packages/mercurial/extensions.py", line 139, in wrap
    util.checksignature(origfn), *args, **kwargs)
  File "/usr/lib64/python2.6/site-packages/mercurial/util.py", line 456, in check
    return func(*args, **kwargs)
  File "/usr/lib64/python2.6/site-packages/hgext/mq.py", line 3337, in mqcommand
    return orig(ui, repo, *args, **kwargs)
  File "/usr/lib64/python2.6/site-packages/mercurial/util.py", line 456, in check
    return func(*args, **kwargs)
  File "/auto/hg/histedit/hg_histedit.py", line 508, in histedit
    hexshort(r), hexshort(created_[0])))
  File "/auto/hg/histedit/hg_histedit.py", line 471, in <lambda>
    hexshort = lambda x: node.hex(x)[:12]
TypeError: b2a_hex() argument 1 must be string or read-only buffer, not None

This is almost certainly fixed in hg 2.5.2. Please upgrade to histedit from hg itself by uninstalling histedit and then upgrading to hg 2.5.2.