code: function notFound(state) {
      logger.log('State not found: {0}', state)
  
      if (options.notFound)
        return setState(leafStates[options.notFound], {})
      else throw new Error ('State "' + state + '" could not be found')
    }
docs: /*
  The state wasn't found
  Transition to the 'notFound' state if the developer specified it or else throw an error.