合并映射抛出'；需要流的对象无效'；rxjs6中的错误

将rxjs从v5迁移到v6后，我在使用mergeMap时遇到一个错误：

of('foobar').pipe(
  mergeMap(() => of('baz'))
).subscribe(console.log);  

错误：

core.js:1598 ERROR TypeError: You provided an invalid object where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.
    at Object.push../node_modules/rxjs/internal/util/subscribeTo.js.exports.subscribeTo (subscribeTo.js:42)
    at Object.subscribeToResult (subscribeToResult.js:7)
    at MergeMapSubscriber.push../node_modules/rxjs/internal/operators/mergeMap.js.MergeMapSubscriber._innerSub (mergeMap.js:132)
    at MergeMapSubscriber.push../node_modules/rxjs/internal/operators/mergeMap.js.MergeMapSubscriber._tryNext (mergeMap.js:129)
    at MergeMapSubscriber.push../node_modules/rxjs/internal/operators/mergeMap.js.MergeMapSubscriber._next (mergeMap.js:112)
    at MergeMapSubscriber.push../node_modules/rxjs/internal/Subscriber.js.Subscriber.next (Subscriber.js:103)
    at Observable._subscribe (scalar.js:5)
    at Observable.push../node_modules/rxjs/_esm5/internal/Observable.js.Observable._trySubscribe (Observable.js:176)
    at Observable.push../node_modules/rxjs/_esm5/internal/Observable.js.Observable.subscribe (Observable.js:161)
    at MergeMapOperator.push../node_modules/rxjs/internal/operators/mergeMap.js.MergeMapOperator.call (mergeMap.js:87)

---

（'baz'）的

是一条流，对吗？那么为什么我会得到这个错误呢
 确保从中正确导入运算符

rxjs/operators

而不是

rxjs/internal/operators

你做的正确吗？从'rxjs'导入{of}；从“rxjs/operators”导入{mergeMap}@siva636 ohhh myyy。。。是rxjs/internal/operators。。我把它换成了rxjs/operators，现在它可以工作了：谢谢你为我节省时间！