code: public UNode toDoc() {
          // Root object is a MAP called "batch".
          UNode batchNode = UNode.createMapNode("batch");
          
          // Add a "docs" node as an array.
          UNode docsNode = batchNode.addArrayNode("docs");
          for (DBObject dbObj : m_dbObjList) {
              docsNode.addChildNode(dbObj.toDoc());
          }
          return batchNode;
      }
docs: Serialize this DBObjectBatch object into a UNode tree and return the root node.
  
  @return  Root node of a UNode tree representing this batch update.