code: func NewState() *State {
  	return &State{
  		store:                        store.NewNilStore(),
  		monitor:                      monitor.NewNilMonitor(),
  		invokeGlobalCallbacksOnFlush: true,
  	}
  }
docs: // NewState returns a new State instance, configured with a nil store and nil
  // monitor. By default, global callbacks that are registered will be invoked
  // when flushing registered metrics.