<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def populate_times(self):
 """ Populates all different meta data times that comes with measurement if they are present. """

        stop_time = self.meta_data.get("stop_time")
        if stop_time:
            stop_naive = datetime.utcfromtimestamp(stop_time)
            self.stop_time = stop_naive.replace(tzinfo=tzutc())

        creation_time = self.meta_data.get("creation_time")
        if creation_time:
            creation_naive = datetime.utcfromtimestamp(creation_time)
            self.creation_time = creation_naive.replace(tzinfo=tzutc())

        start_time = self.meta_data.get("start_time")
        if start_time:
            start_naive = datetime.utcfromtimestamp(start_time)
            self.start_time = start_naive.replace(tzinfo=tzutc())