public TvShow getTvShowById(String tvShowId) throws TvShowNotFoundException {
    TvShow result = searchTvShowById(tvShowId);
    if (result == null) {
      throw new TvShowNotFoundException(
          "The identifier" + tvShowId + "is not associated to any TvShow");
    }
    return result;
  }
Search a TvShow using a tv show identifier.

We should return a clone of TvShow objects inside catalog because all this data is in
memory and anyone can change it. But, this is just a sample!

@param tvShowId used to search inside the catalog.
@return a TvShow that matches with the parameter passed as identifier.
parameter.
app/src/main/java/com/github/pedrovgs/effectiveandroidui/domain/tvshow/Catalog.java