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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def file_detector(self, detector):
 """ Set the file detector to be used when sending keyboard input. By default, this is set to a file detector that does nothing. see FileDetector see LocalFileDetector see UselessFileDetector :Args: - detector: The detector to use. Must not be None. """

        if detector is None:
            raise WebDriverException("You may not set a file detector that is null")
        if not isinstance(detector, FileDetector):
            raise WebDriverException("Detector has to be instance of FileDetector")
        self._file_detector = detector