public Collection<TvShow> getTvShows() {
    return (Set<TvShow>) ((LinkedHashSet<TvShow>) tvShows).clone();
  }
We should return a full clone of TvShow objects inside catalog because all this data is in
memory and anyone can change it if we don't return only copies, but this is just a sample!

@return all available TvShow in the catalog.
app/src/main/java/com/github/pedrovgs/effectiveandroidui/domain/tvshow/Catalog.java