Use FObjectFinder with TSubClassof variable?

To those who are looking for a way even though time has passed.

Use FClassFinder

static ConstructorHelpers::FClassFinder<UUserWidget> ErrWdgtCntnt(TEXT("/Game/UI/Widgets/Common/WGT_Warning'"));
if (ErrWdgtCntnt.Succeeded())
{
	ErrorDialogWidget = ErrWdgtCntnt.Class;
}