How to use the @angular/animations.AnimationMetadataType.Transition function in @angular/animations

metadata.definitions.forEach(def => {
      this._resetContextStyleTimingState(context);
      if (def.type == AnimationMetadataType.State) {
        const stateDef = def as AnimationStateMetadata;
        const name = stateDef.name;
        name.split(/\s*,\s*/).forEach(n => {
          stateDef.name = n;
          states.push(this.visitState(stateDef, context));
        });
        stateDef.name = name;
      } else if (def.type == AnimationMetadataType.Transition) {
        const transition = this.visitTransition(def as AnimationTransitionMetadata, context);
        queryCount += transition.queryCount;
        depCount += transition.depCount;
        transitions.push(transition);
      } else {
        context.errors.push(
            'only state() and transition() definitions can sit inside of a trigger()');
      }
    });
    const ast = new TriggerAst(metadata.name, states, transitions);

function createFallbackTransition(
    triggerName: string,
    states: {[stateName: string]: AnimationStateStyles}): AnimationTransitionFactory {
  const matchers = [(fromState: any, toState: any) => true];
  const animation: SequenceAst = {type: AnimationMetadataType.Sequence, steps: [], options: null};
  const transition: TransitionAst = {
    type: AnimationMetadataType.Transition,
    animation,
    matchers,
    options: null,
    queryCount: 0,
    depCount: 0
  };
  return new AnimationTransitionFactory(triggerName, transition, states);
}