Logpull cookies field is blank

When using Logpull we never receive any cookies. We have tried adding custom fields as one would do with logpush → https://developers.cloudflare.com/logs/reference/custom-fields/

But no luck. We tried using both the api and the client dashboard but this feature of creating custom fields seems only to work with logpush not logpull (the docs explicitly say logpush and never mention logpull).

Has anyone been able to get cookies out of logpull? If so is their a trick to enabling them?