Which plugin or extension has the filternulls() function for 7.5? Thanks....

You could use the OOTB functionality and try reject(fn!isnull, {pv!list}). forum.appian.com/.../Looping_Functions

Correct. However I need the filternull() function itself so existing stuff works without mods.

It would be the same plugin you already have in your environment. Filternulls was I believe part of a set of doforeach plugin. Since that is now deprecated, make sure you put replacement of it with out of the box looping functions on your technical backlog.