Using explore to find empty arrays

One of our services produces logs of the form:

{
  "level": \d+
  ...
  "data": {
    "items": [ {...item}, {...item} ...],
    ...
    "otherKey": null
  }
  "msg": "searchable log message"
}

note that the value for otherKey is not quoted

how would I find logs where data.items is an empty array? I can’t find any sort of array length filters.

How would I find where data.otherKey is null? | json key="data.otherKey" | key = null results in a parsing error.