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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 get_file_extension(filename):
 """ Return the extension if the filename has it. None if not. :param filename: The filename. :return: Extension or None. """

    filename_x = filename.split('.')
    if len(filename_x) > 1:
        if filename_x[-1].strip() is not '':
            return filename_x[-1]
    return None