qlog AttributeError: 'NoneType' object has no attribute 'startswith'

[Max Bowsher]

bzr.dev, qbzr trunk, Ubuntu maverick. On collapsing a merged part of a qlog tree such that the currently selected revision disappears from view, I get:

bzr: ERROR: exceptions.AttributeError: 'NoneType' object has no attribute 'startswith'

Traceback (most recent call last):
  File "/home/maxb/.bazaar/plugins/qbzr/lib/util.py", line 870, in decorate
    run_in_loading_queue(f, *args, **kargs)
  File "/home/maxb/.bazaar/plugins/qbzr/lib/util.py", line 882, in run_in_loading_queue
    f(*args, **kargs)
  File "/home/maxb/.bazaar/plugins/qbzr/lib/uifactory.py", line 32, in decorate
    r = f(*args, **kargs)
  File "/home/maxb/.bazaar/plugins/qbzr/lib/log.py", line 642, in load_delta
    if (revid.startswith(CURRENT_REVISION) and
AttributeError: 'NoneType' object has no attribute 'startswith'