code: protected void addParentKeyToDocument(String parentId, Document currentDoc, Class<?> clazz) {
          // if (parentId != null)
          if (clazz != null && parentId != null) {
              Field luceneField =
                  new Field(IndexingConstants.PARENT_ID_FIELD, parentId, Field.Store.YES, Field.Index.ANALYZED_NO_NORMS);
              currentDoc.add(luceneField);
              Field fieldClass =
                  new Field(IndexingConstants.PARENT_ID_CLASS, clazz.getCanonicalName().toLowerCase(), Field.Store.YES,
                      Field.Index.ANALYZED);
              currentDoc.add(fieldClass);
          }
      }
docs: Index parent key.
  
  @param parentId
  the parent id
  @param currentDoc
  the current doc
  @param clazz
  the clazz