下面是rqdatac包出错，我没动任何代码。
Traceback (most recent call last):
File "C:\vnstudio\lib\site-packages\vnpy\trader\ui\mainwindow.py", line 270, in open_widget
widget = widget_class(self.main_engine, self.event_engine)
File "C:\vnstudio\lib\site-packages\vnpy\app\cta_backtester\ui\widget.py", line 43, in init
self.backtester_engine.init_engine()
File "C:\vnstudio\lib\site-packages\vnpy\app\cta_backtester\engine.py", line 61, in init_engine
self.init_rqdata()
File "C:\vnstudio\lib\site-packages\vnpy\app\cta_backtester\engine.py", line 67, in init_rqdata
result = rqdata_client.init()
File "C:\vnstudio\lib\site-packages\vnpy\trader\rqdata.py", line 64, in init
df = rqdata_all_instruments()
File "C:\vnstudio\lib\site-packages\rqdatac\decorators.py", line 131, in wrap
return func(args, **kwargs)
File "C:\vnstudio\lib\site-packages\rqdatac\services\basic.py", line 319, in all_instruments
ins_ret = filter(cond, _all_instruments_list(market))
File "C:\vnstudio\lib\site-packages\rqdatac\decorators.py", line 111, in wrapper
value = user_function(args, **kwargs)
File "C:\vnstudio\lib\site-packages\rqdatac\services\basic.py", line 107, in _all_instruments_list
return [Instrument(i) for i in get_client().execute("all_instruments", market)]
TypeError: 'NoneType' object is not iterable
