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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_all_stations(self, station_type=None):
 """Returns information of all stations. @param<optional> station_type: ['mainline', 'suburban', 'dart'] """

        params = None
        if station_type and station_type in STATION_TYPE_TO_CODE_DICT:
            url = self.api_base_url + 'getAllStationsXML_WithStationType'
            params = {
                'stationType': STATION_TYPE_TO_CODE_DICT[station_type]
            }
        else:
            url = self.api_base_url + 'getAllStationsXML'

        response = requests.get(
            url, params=params, timeout=10)

        if response.status_code != 200:
            return []

        return self._parse_station_list(response.content)