code: function isValidTransition (link, context) {
      var isValid = true;
  
      if (!(PromisePipe.envTransitions[context._env] && PromisePipe.envTransitions[context._env][link._env])) {
        if (!isSystemTransition(link._env)) {
          isValid = false;
        }
      }
      return isValid;
    }
docs: Check valid is transition