bzr: ERROR: The branch http://svn.apache.org/repos/asf/subversion/trunk has no revision None.

Trying to branch the subversion trunk up on svn.apache.org fails with:
   bzr: ERROR: The branch http://svn.apache.org/repos/asf/subversion/trunk has no revision None.

The command I used was:
   bzr branch http://svn.apache.org/repos/asf/subversion/trunk subversion -Derror

I also removed the cache, just to see if that was a problem, but it failed the same way.

Here's the traceback... unfortunately, it's not terribly useful:

bzr: ERROR: bzrlib.errors.BzrCommandError: The branch http://svn.apache.org/repos/asf/subversion/trunk has no revision None.

Traceback (most recent call last):
  File "/Users/jszakmeister/Library/Python/2.6/site-packages/bzrlib/commands.py", line 853, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/Users/jszakmeister/Library/Python/2.6/site-packages/bzrlib/commands.py", line 1055, in run_bzr
    ret = run(*run_argv)
  File "/Users/jszakmeister/Library/Python/2.6/site-packages/bzrlib/commands.py", line 661, in run_argv_aliases
    return self.run_direct(**all_cmd_args)
  File "/Users/jszakmeister/Library/Python/2.6/site-packages/bzrlib/commands.py", line 665, in run_direct
    return self._operation.run_simple(*args, **kwargs)
  File "/Users/jszakmeister/Library/Python/2.6/site-packages/bzrlib/cleanup.py", line 122, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/Users/jszakmeister/Library/Python/2.6/site-packages/bzrlib/cleanup.py", line 156, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/Users/jszakmeister/Library/Python/2.6/site-packages/bzrlib/builtins.py", line 1238, in run
    raise errors.BzrCommandError(msg)
BzrCommandError: The branch http://svn.apache.org/repos/asf/subversion/trunk has no revision None.