selenium-file-input

... snip ...

  File "/<snip>/lib/python2.7/site-packages/selenium/webdriver/remote/webelement.py", line 347, in send_keys
    self._execute(Command.SEND_KEYS_TO_ELEMENT, {'value': keys_to_typing(value)})
  File "/<snip>/lib/python2.7/site-packages/selenium/webdriver/remote/webelement.py", line 494, in _execute
    return self._parent.execute(command, params)
  File "/<snip>/lib/python2.7/site-packages/selenium/webdriver/remote/webdriver.py", line 236, in execute
    self.error_handler.check_response(response)
  File "/<snip>/lib/python2.7/site-packages/selenium/webdriver/remote/errorhandler.py", line 192, in check_response
    raise exception_class(message, screen, stacktrace)
WebDriverException: Message: Expected [object Undefined] undefined to be a string
Build info: version: '3.3.1', revision: '5234b32', time: '2017-03-10 09:04:52 -0800'
System info: host: 'selenium-hub', ip: '127.0.1.1', os.name: 'Linux', os.arch: 'amd64', os.version: '4.4.0-71-generic', java.version: '1.8.0_121'
Driver info: org.openqa.selenium.firefox.FirefoxDriver
Capabilities [{moz:profile=/tmp/rust_mozprofile.nt4AGy3FiE8R, rotatable=false, timeouts={implicit=0, pageLoad=300000, script=30000}, pageLoadStrategy=normal, platform=ANY, specificationLevel=0, moz:accessibilityChecks=false, acceptInsecureCerts=false, browserVersion=53.0, platformVersion=4.4.0-71-generic, moz:processID=31504, browserName=firefox, platformName=linux}]