Records the given timestamp.

        :param name: a counter name of Timestamp type.

        :param value: a timestamp to record.

def timestamp(self, name, value):
        """
        Records the given timestamp.

        :param name: a counter name of Timestamp type.

        :param value: a timestamp to record.
        """
        counter = self.get(name, CounterType.Timestamp)
        counter.time = value if value != None else datetime.datetime.utcnow()
        self._update()