code: private void addChunkId(Document dbObject) {
          List<String> chunkIds = new ArrayList<>();
          int chunkStart = (Integer) dbObject.get("start") / MongoDBCollectionConfiguration.VARIATION_CHUNK_SIZE;
          int chunkEnd = (Integer) dbObject.get("end") / MongoDBCollectionConfiguration.VARIATION_CHUNK_SIZE;
          String chunkIdSuffix = MongoDBCollectionConfiguration.VARIATION_CHUNK_SIZE / 1000 + "k";
          for (int i = chunkStart; i <= chunkEnd; i++) {
              if (dbObject.containsKey("chromosome")) {
                  chunkIds.add(dbObject.get("chromosome") + "_" + i + "_" + chunkIdSuffix);
              } else {
                  chunkIds.add(dbObject.get("sequenceName") + "_" + i + "_" + chunkIdSuffix);
              }
          }
          dbObject.put("_chunkIds", chunkIds);
      }
docs: by MongoDBCellbaseLoader must be replaced by an appropriate method in this adaptor