@Override
      public void close() {
        if (next != null) {
          releaseNode(next);
          next = null;
        }
      }
The interface to start the traversal. The node process should be defined before traversal by
overriding or implement concerned methods.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/traverser/Traverser.java