你好downloader运行报这个错，能帮忙看下吗

[Winemusic]

DEBUG 2019-03-11 19:17:38,154 remote_connection 17539 140576538605376 Finished Request
ERROR 2019-03-11 19:17:38,154 downloaders 17539 140576538605376 Message: Expected [object Undefined] undefined to be a string
Traceback (most recent call last):
File "/root/wechat-spider/wechat/downloaders.py", line 100, in download_wechat
self.visit_wechat_index(wechatid)
File "/root/wechat-spider/wechat/downloaders.py", line 171, in visit_wechat_index
element_querybox.send_keys(wechatid, Keys.ARROW_DOWN)
File "/usr/lib/python2.7/site-packages/selenium/webdriver/remote/webelement.py", line 479, in send_keys
'value': keys_to_typing(value)})
File "/usr/lib/python2.7/site-packages/selenium/webdriver/remote/webelement.py", line 633, in _execute
return self._parent.execute(command, params)
File "/usr/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.py", line 321, in execute
self.error_handler.check_response(response)
File "/usr/lib/python2.7/site-packages/selenium/webdriver/remote/errorhandler.py", line 242, in check_response
raise exception_class(message, screen, stacktrace)
InvalidArgumentException: Message: Expected [object Undefined] undefined to be a string