code: def get_file_extension(filename):
      
      filename_x = filename.split('.')
      if len(filename_x) > 1:
          if filename_x[-1].strip() is not '':
              return filename_x[-1]
      return None
docs: Return the extension if the filename has it. None if not.
  
      :param filename: The filename.
      :return: Extension or None.