Possible PART crash?

[IcEBnd]

[11:02:19] freenode RECV: PING :wilhelm.freenode.net
[11:02:19] freenode SENT: PONG :wilhelm.freenode.net
[11:02:21] freenode RECV: :ptrrr!~peter@46.226.154.181 PART #c++.se
Traceback (most recent call last):
File "main.py", line 46, in
pdb.run(Tick())
File "main.py", line 34, in Tick
bot.tick()
File "/home/tech/ice/riverbot/ircbot.py", line 220, in tick
client.tick()
File "/home/tech/ice/riverbot/ircclient/ircclient.py", line 294, in tick
self.message_handlers[m.group(3)](m.group%280, 1, 2, 3, 4, 5%29)
File "/home/tech/ice/riverbot/ircclient/ircclient.py", line 216, in on_part
nick_lists[channel].remove(source_nick)
NameError: global name 'nick_lists' is not defined
/bin/sh: 1: aspell: not found
[11:12:22] Could not load data from file 'data/festern_bbq.txt' :(