bzr->git: keep empty directories

hello,

when converting a repo from bzr to git:

mkdir freeplane-git1
cd freeplane-git1
git init .
bzr fast-export --plain --export-marks=../marks.bzr ../trunk/ | git fast-import --export-marks=../marks.git
git checkout

Empty directories are not contained in the git working index. This is
because of the --plain option, which "Excludes metadata to maximise
interoperability" and thus does not support empty directories
(http://doc.bazaar.canonical.com/plugins/en/fastimport-plugin.html).

However, when I use "--no-plain" (which according to above documentation
exports empty directories), git cannot handle it:

$ ./freeplane2git.sh 
Initialized empty Git repository in /home/felix/git/freeplane-git1/.git/
15:56:09 Calculating the revisions to include ...
15:56:09 Starting export of 4290 revisions ...
fatal: This version of fast-import does not support feature commit-properties.
fast-import: dumping crash report to .git/fast_import_crash_3915
bzr: broken pipe

I already tried to hack bzr-fastimport's exporter.py so that it does not
emit commit properties but emits empty directories but i was not
successful.

So is there another way to preserve empty directories or shall I report
a bug on bzr fast-export?

Many thanks in advance!
-- 
Felix Natter