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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 _normalized_serial(self):
 """Normalized serial name for usage in log filename. Some Android emulators use ip:port as their serial names, while on Windows `:` is not valid in filename, it should be sanitized first. """

        if self._serial is None:
            return None
        normalized_serial = self._serial.replace(' ', '_')
        normalized_serial = normalized_serial.replace(':', '-')
        return normalized_serial