code: def getNewestCompleteTime(self):
          
          bldrid = yield self.getBuilderId()
          completed = yield self.master.data.get(
              ('builders', bldrid, 'buildrequests'),
              [resultspec.Filter('complete', 'eq', [False])],
              order=['-complete_at'], limit=1)
          if completed:
              return completed[0]['complete_at']
          else:
              return None
docs: Returns the complete_at of the latest completed build request for
          this builder, or None if there are no such build requests.
  
          @returns: datetime instance or None, via Deferred