Comment 2 for bug 242175

FWIW, the current error worse: you get a traceback:

bzr: ERROR: exceptions.ValueError: WorkingTree.set_root_id with fileid=None

Traceback (most recent call last):
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 923, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 1123, in run_bzr
    ret = run(*run_argv)
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 688, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/home/andrew/code/bzr/bzrlib/commands.py", line 710, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/cleanup.py", line 135, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/cleanup.py", line 165, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/builtins.py", line 1494, in run
    show_base=show_base)
  File "/home/andrew/code/bzr/bzrlib/workingtree.py", line 2308, in update
    return self._update_tree(old_tip, change_reporter, revision, show_base)
  File "/home/andrew/code/bzr/bzrlib/mutabletree.py", line 49, in tree_write_locked
    return unbound(self, *args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/workingtree.py", line 2365, in _update_tree
    self.set_root_id(to_root_id)
  File "/home/andrew/code/bzr/bzrlib/mutabletree.py", line 49, in tree_write_locked
    return unbound(self, *args, **kwargs)
  File "/home/andrew/code/bzr/bzrlib/workingtree.py", line 2221, in set_root_id
    'WorkingTree.set_root_id with fileid=None')
ValueError: WorkingTree.set_root_id with fileid=None

Tracebacks are bad, bumping this up to High.