code: public org.apache.lucene.search.Sort sort(Schema schema) {
          return sort == null ? null : sort.sort(schema);
      }
docs: Returns the Lucene {@link org.apache.lucene.search.Sort} represented by this {@link Sort} using the specified
  {@link Schema}. Maybe {@code null} meaning no sorting.
  
  @param schema A {@link Schema}.
  @return The Lucene {@link org.apache.lucene.search.Sort} represented by this {@link Sort} using {@code schema}.