JQL Search for Estimated Time is NULL / BLANK

Is there a way to do a query/filter on estimatedTime that has not yet been entered?

I was able to find this information:

https://support.smartbear.com/zephyr-scale-server/docs/en/jql-functions.html#UUID-bb04c337-22d6-fee6-7703-b4515a68234c_N1697097036420

I saw this example in the documentation and it seems to work as expected, but is limited to only filter an exact value:

project = MGS and issue in coveredByTestCasesHavingField("estimatedTime", "03:00")

I would like to use this to find all issues with test cases where the estimatedTime has not yet been entered.  I tried using synatax of ("estimatedTime", NULL) and ("estimatedTime", BLANK) and these did not work.  I also used ("estimatedTime", 00:00) but this is not the same as it not being entered.

As a follow-on related question: is there a way to use this to search for estimatedTime > 00:05 or < 00:05 as an example?