bsn_error undefined

[blp]

In testing OVS with OFTest, I came across the following exception when OVS sent an unexpected error message. It happens in a number of tests:

groups.GroupAddIndirectWeight ... Exception in thread Thread-2:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/home/blp/nicira/oftest/src/python/oftest/controller.py", line 451, in run
    if self._socket_ready_handle(s) == -1:
  File "/home/blp/nicira/oftest/src/python/oftest/controller.py", line 380, in _socket_ready_handle
    self._pkt_handle(pkt)
  File "/home/blp/nicira/oftest/src/python/oftest/controller.py", line 298, in _pkt_handle
    if msg.version >= 3 and isinstance(msg, ofp.message.bsn_error):
AttributeError: 'module' object has no attribute 'bsn_error'