退出ipython时出现隐秘错误

Question

退出ipython时出现以下错误：

In [3]: 
Do you really want to exit ([y]/n)? y

Exception in thread Thread-1 (most likely raised during interpreter shutdown):
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
  File "/usr/lib/python2.7/threading.py", line 763, in run
  File "/root/myproject/venv/local/lib/python2.7/site-packages/scrapy/crawler.py", line 130, in start_reactor
  File "/root/myproject/venv/local/lib/python2.7/site-packages/twisted/internet/base.py", line 1192, in run
  File "/root/myproject/venv/local/lib/python2.7/site-packages/twisted/internet/base.py", line 1206, in mainLoop
<type 'exceptions.AttributeError'>: 'NoneType' object has no attribute 'msg'

我重新启动了，它不再发生了。这是scrapy shell命令中的ipython REPL。在REPL中，我运行的代码没有错误。