events without anonid

[camilleanne]

Seeing a lot of events pop up with a null anonid field -- doesn't seem to be correlated to mapid

{ event: 'layer.tileload',
  url: 'https://b.tiles.mapbox.com/v4/{mapid}/15/9642/12273@2x.png?access_token={token}',
  timeTaken: 220.9569999249652,
  version: 1,
  created: 1430266980563,
  instance: '436d84756b8f1325631c8ae526fd59d5',
  anonid: null,
  userAgent: 'Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.90 Safari/537.36' 
}