'Return a GrrMessage instance from the transaction log or None.'

def GetTransactionLog(self):

    try:
        with open(self._GetLogFilename(), 'rb') as fd:
            data = fd.read(self.max_log_size)
    except (IOError, OSError):
        return
    try:
        if data:
            return rdf_flows.GrrMessage.FromSerializedString(data)
    except (message.Error, rdfvalue.Error):
        return
