validators/not-equal: Use isNone() instead of null check
validators/not-equal: Use isNone() instead of null check

RBE-Avionik/skylines,skylines-project/skylines,RBE-Avionik/skylines,shadowoneau/skylines,shadowoneau/skylines,RBE-Avionik/skylines,Turbo87/skylines,Turbo87/skylines,Harry-R/skylines,shadowoneau/skylines,Harry-R/skylines,RBE-Avionik/skylines,skylines-project/skylines,Harry-R/skylines,shadowoneau/skylines,Harry-R/skylines,Turbo87/skylines,Turbo87/skylines,skylines-project/skylines,skylines-project/skylines