Missing fields in wtm.attrack.keysv2

[philipp-classen]

To be investigated: clients sometimes send keysv2 messages with missing fields:

{
  "action": "wtm.attrack.keysv2",
  "anti-duplicates": 6545610,
  "channel": "firefox-desktop",
  "payload": {
    "data": [
      {
        "ts": "20241030",
        "site": "undefined", <-- ??
        "tokens": [
          [
            "undefined",   <--- ??
            null           <--- ??
          ]
        ]
      }
    ],
    "ver": "0.103",
    "day": "2024-10-28",
    "ts": "2024103007",
    "ctry": "us"
  },
  "ts": "20241030",
  "type": "wtm.request",
  "userAgent": "firefox"
}