Fix API Bug (fail on empty assignees) (#8873)

Fix API Bug (fail on empty assignees) (#8873)

* keep sure if assigneeIDs == nil -> do nothing

* fix #8872

* Revert "keep sure if assigneeIDs == nil -> do nothing"

-> go handle it itself preaty well

This reverts commit e72d94129c4666d5151f6131cb2f8c1de127d9d0.

* clarity comparson

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>
* simplify

* Update models/issue_assignees.go

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>
* Update issue_assignees.go

* simplify more

* add --if oneAssignee != ""-- again

* Update models/issue_assignees.go

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>
* CI.restart()

* Update issue_assignees.go

* add Test for GetUserIDsByNames

* add Test for MakeIDsFromAPIAssigneesToAdd

* fix test