public ParallelSystem(SystemRunner <TState> runner, params ISystem <TState>[] systems) : this(null, runner, systems)
{
}
public ParallelSystem(ISystem <TState> mainSystem, SystemRunner <TState> runner, params ISystem <TState>[] systems) : base(runner)
{
this.mainSystem = mainSystem;
this.systems = systems ?? ArrayExtension.EmptyArray <ISystem <TState> > .Value;
}