'Return the threshold dict.
If stat_name is None, return the threshold for all plugins (dict of Threshold*)
Else return the Threshold* instance for the given plugin'

def get(self, stat_name=None):

    if (stat_name is None):
        return self._thresholds
    if (stat_name in self._thresholds):
        return self._thresholds[stat_name]
    else:
        return {}
