Fix for possible NullReferenceException
Fix for possible NullReferenceException

HermanEldering/oxyplot,GeertvanHorrik/oxyplot,Sbosanquet/oxyplot,TheAlmightyBob/oxyplot,Isolocis/oxyplot,br111an/oxyplot,freudenthal/oxyplot,shoelzer/oxyplot,jeremyiverson/oxyplot,shoelzer/oxyplot,oxyplot/oxyplot,svendu/oxyplot,objorke/oxyplot,as-zhuravlev/oxyplot_wpf_fork,Mitch-Connor/oxyplot,Kaplas80/oxyplot,olegtarasov/oxyplot,H2ONaCl/oxyplot,freudenthal/oxyplot,mattleibow/oxyplot,as-zhuravlev/oxyplot_wpf_fork,lynxkor/oxyplot,HermanEldering/oxyplot,H2ONaCl/oxyplot,shoelzer/oxyplot,objorke/oxyplot,Jofta/oxyplot,jeremyiverson/oxyplot,freudenthal/oxyplot,bbqchickenrobot/oxyplot,DotNetDoctor/oxyplot,svendu/oxyplot,as-zhuravlev/oxyplot_wpf_fork,br111an/oxyplot,br111an/oxyplot,Kaplas80/oxyplot,Rustemt/oxyplot,lynxkor/oxyplot,Mitch-Connor/oxyplot,olegtarasov/oxyplot,DotNetDoctor/oxyplot,Rustemt/oxyplot,bbqchickenrobot/oxyplot,lynxkor/oxyplot,Jonarw/oxyplot,objorke/oxyplot,zur003/oxyplot,NilesDavis/oxyplot,TheAlmightyBob/oxyplot,bbqchickenrobot/oxyplot,Sbosanquet/oxyplot,Sbosanquet/oxyplot,svendu/oxyplot,mattleibow/oxyplot,jeremyiverson/oxyplot,GeertvanHorrik/oxyplot,Mitch-Connor/oxyplot,TheAlmightyBob/oxyplot,ze-pequeno/oxyplot,H2ONaCl/oxyplot,GeertvanHorrik/oxyplot,Rustemt/oxyplot