code: @SuppressWarnings({"WeakerAccess", "unused"}) // For library users
      @NonNull
      public Searcher setIndex(@NonNull String indexName) {
          if (client == null) {
              throw new IllegalStateException("This method requires an Algolia Index and not a custom Searchable");
          }
          searchable = client.getIndex(indexName);
          query.setPage(0);
          return this;
      }
docs: Changes the targeted index for future queries.
  <p>
  <b>Be aware that as index ordering may differ, this method will reset the current page to 0.</b>
  You may want to use {@link Searcher#reset} to reinitialize the helper to an empty state.
  
  @param indexName name of the new index.
  @return this {@link Searcher} for chaining.