def next_state(event_name)
      transition = transitions.select{|t| t.is_transition_for?(event_name, @subject.send(state_method))}.first
      transition ? transition.to : nil
    end
def next_state(event_name)
      transition = transitions.select{|t| t.is_transition_for?(event_name, @subject.send(state_method))}.first
      transition ? transition.to : nil
    end
Returns the next state for the subject for event_name