code: int[] getDocumentNumbers(MultiIndexReader reader, int[] docNumbers) throws IOException {
          int doc = reader.getDocumentNumber(this);
          if (doc == -1) {
              return EMPTY;
          } else {
              if (docNumbers.length == 1) {
                  docNumbers[0] = doc;
                  return docNumbers;
              } else {
                  return new int[]{doc};
              }
          }
      }
docs: {@inheritDoc}