Not operator (!=) not functional when searching epics

Summary

Search for Epics with the != operator is not possible.

Steps to reproduce

1. Search for labels != ~"group::import" includes epics with ~"group::import" label
2. Search for labels=None includes epics with labels
3. Search for author != @NicoleSchwartz includes epics with @NicoleSchwartz as author

What is the current bug behavior?

Not operator (!=) is ignored for epics.

What is the expected correct behavior?

Not operator (!=) is observed for epics.

Relevant logs and/or screenshots