cvs2svn failure (traceback in pass 4)

I get this backtrace when running cvs2svn on my debhelper cvs
repository. The command line was:

cvs2svn -s svnroot ~cvs/repository/joey-cvs/public/packages/debhelper

After a while, it crashes:

finishing 'debian_version_4_1_32' as branch
finishing 'potato' as branch
finishing 'debian_version_4_0_10' as branch
finishing 'upstream_version_1_1_20' as branch
finishing 'upstream_version_0_77' as branch
finishing 'upstream_version_0_74' as branch
finishing 'upstream_version_1_1_23' as branch
finishing 'upstream_version_0_72' as branch
finishing 'upstream_version_0_73' as branch
finishing 'upstream_version_0_70' as branch
finishing 'upstream_version_0_71' as branch
finishing 'upstream_version_0_78' as branch
finishing 'upstream_version_0_79' as branch
Finishing tags:
finishing 'upstream_version_1_0' as tag
finishing 'debian_version_2_0_57' as tag
finishing 'upstream_version_1_2_8' as tag
finishing 'debian_version_4_1_35' as tag
finishing 'upstream_version_0_92' as tag
Traceback (most recent call last):
  File "/usr/bin/cvs2svn", line 2236, in ?
    main()
  File "/usr/bin/cvs2svn", line 2232, in main
    convert(ctx, start_pass=start_pass)
  File "/usr/bin/cvs2svn", line 2111, in convert
    _passes[i](ctx)
  File "/usr/bin/cvs2svn", line 2075, in pass4
    sym_tracker.finish(dumper, ctx)
  File "/usr/bin/cvs2svn", line 1697, in finish
    self.fill_tag(dumper, ctx, name, [1])
  File "/usr/bin/cvs2svn", line 1644, in fill_tag
    self.fill_name(dumper, ctx, tag, 1, jit_new_rev)
  File "/usr/bin/cvs2svn", line 1631, in fill_name
    is_tag, jit_new_rev)
  File "/usr/bin/cvs2svn", line 1535, in copy_descend
    next_src, next_dst, is_tag, jit_new_rev)
  File "/usr/bin/cvs2svn", line 1510, in copy_descend
    dumper.copy_path(src_path, parent_rev, copy_dst, val)
  File "/usr/bin/cvs2svn", line 960, in copy_path
    entries)
  File "/usr/bin/cvs2svn", line 661, in change_path
    for ent in new_val.keys():
AttributeError: 'NoneType' object has no attribute 'keys'

I'm using the debian package of subversion 0.26 and python 2.2.3.
I can make this repository available as a tarball if that would help.

-- 
see shy jo