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

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);
}