"Does Not Exist" (DNE) property filter for Keen IO analysis calls

I'm trying to write a query against my Keen IO collection of pageviews, I really need a particular property to be filtered out. That is a filter for whenever a referral_URL "does not exist" (DNE).

I noticed there is a full list of other filter operations, but no DNE. I tried "Equal to" "Null" but it didn't do it for me.

List of Filter Operations: https://keen.io/docs/api/#operator-definitions

Is this possible?

Use the "Property Exists" operator. You will find it about half-way down the list of operators in your screenshot.

However, once you select that operator, you will see the value on the right default to "True". This would actually be the opposite of what you're after. To get DNE, you need to set the boolean value to "False".

You're correct in your findings that the "Equal to" "Null" doesn't work in the same way as DNE. Behaviorally, that is a string comparison, so events that do not have a value will not satisfy that filter.