bzr diff --using <whatever> crashes if no commit has been made

Steps to recreate;

- Create a new directory for project and change into it.
- Do "bzr init".
- Add a file "echo 'hello' > a.txt"
- Add it to bzr : "bzr add a.txt".
- Run "bzr diff --using mgdiff"

Traceback looks like:

bzr: ERROR: exceptions.StopIteration:

Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 834, in run_bzr_catch_errors
    return run_bzr(argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 790, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 492, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/home/erikd/.bazaar/plugins/trunk/__init__.py", line 78, in run
  File "/home/erikd/.bazaar/plugins/trunk/controller.py", line 61, in run
  File "/home/erikd/.bazaar/plugins/trunk/controller.py", line 185, in compare_using
  File "/home/erikd/.bazaar/plugins/trunk/tempdir.py", line 40, in write_stuff
  File "/home/erikd/.bazaar/plugins/trunk/tempdir.py", line 51, in write_tree
  File "/usr/lib/python2.5/site-packages/bzrlib/export/__init__.py", line 97, in export
    return _exporters[format](tree, dest, root)
  File "/usr/lib/python2.5/site-packages/bzrlib/export/__init__.py", line 61, in _loader
    return func(tree, dest, root)
  File "/usr/lib/python2.5/site-packages/bzrlib/export/dir_exporter.py", line 40, in dir_exporter
    entries.next() # skip root
StopIteration

bzr 1.2.0.candidate.1 on python 2.5.2.final.0 (linux2)
arguments: ['/usr/bin/bzr', 'diff', '--using', 'meld']
encoding: 'ANSI_X3.4-1968', fsenc: 'ANSI_X3.4-1968', lang: 'en_AU.UTF-8'
plugins:
  bzr_difftools /home/erikd/.bazaar/plugins/bzr_difftools [0.91.0]
  bzrtools /usr/lib/python2.5/site-packages/bzrlib/plugins/bzrtools [1.2.0]
  gtk /usr/lib/python2.5/site-packages/bzrlib/plugins/gtk [0.93.0]
  lastlog /home/erikd/.bazaar/plugins/lastlog [unknown]
  launchpad /usr/lib/python2.5/site-packages/bzrlib/plugins/launchpad [unknown]
  lessdiff /home/erikd/.bazaar/plugins/lessdiff [unknown]
  lesslog /home/erikd/.bazaar/plugins/lesslog [unknown]
  signing /home/erikd/.bazaar/plugins/signing [unknown]
*** Bazaar has encountered an internal error.
    Please report a bug at https://bugs.launchpad.net/bzr/+filebug
    including this traceback, and a description of what you
    were doing when the error occurred.