We must check whether outputs or inputVars are non-empty before
accessing them.
This amends commit 68866b1a.
Task-number: QTBUG-79178
Change-Id: Iecf6dc705bac9bef5133ae2e5ceeace5f859f175
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>
(cherry picked from commit d3d5eadf2432ddc874eabbb2d2f56c4b9ff8830f)