How to handle errors in rxJava 2 correctly?

The project consists of 3 parts: data ,presentation,domain In data, there is a repository that receives data and transforms it into an object for the domain and, in principle, it does not matter any further. So, how do you handle the error if the data did not come? How to handle errors in Rx in general? applied such

  @Override public Observable<AuthorizationModel> getPostById(String postId) { return restClient.getAutrorizationApi(postId) .map(this.authorizationEntityDataMapper::transform) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()); }