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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 GetWindowsEventMessage(self, log_source, message_identifier):
 """Retrieves the message string for a specific Windows Event Log source. Args: log_source (str):
 Event Log source, such as "Application Error". message_identifier (int):
 message identifier. Returns: str: message string or None if not available. """

    database_reader = self._GetWinevtRcDatabaseReader()
    if not database_reader:
      return None

    if self._lcid != self.DEFAULT_LCID:
      message_string = database_reader.GetMessage(
          log_source, self.lcid, message_identifier)
      if message_string:
        return message_string

    return database_reader.GetMessage(
        log_source, self.DEFAULT_LCID, message_identifier)