Reference qualifier is blocking NULL though not specified when a condition is configured

[Les1]

So an odd or confusing behavior that i'd appreciate another set of eyes to concur and/or help explain the behavior:

i've got a simple reference qualifier for a variable looking at the sys_user table, as part of a catalog item var set (screenshot provided)

Whenever i include "employee number does not contain"  instead of JUST applying the condition it also includes blocking if "Employee Number is empty"   .. i dont know why since i did not specify that and actually wanted to include if Employee Number is empty at least until i DONT want to include it.  

I can workaround this by adding "or employee number is empty"

anyway, if someone else could help concur that apparently this is normal behavior and if someone happens to understand why, that'd be helpful to understand as it doesn't seem intuitive.

[Tony Chatfield1 · Accepted solution]

Hi, I agree that the behavior is a little unexpected and counter intuitive, but similar can be seen in an OOB PDI UI. From Incident list try right clicking a field like Caller and selecting filter out, then expand the resulting filter - it will have an additional condition of Call is NULL appended by the platform.

The behavior is explained\covered in this KB article

https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0715430

[Les1]

Thanks Tony, that's the info I was needing. So just need to always have a "OR is empty" included if null is expected.