code: public UNode getMember(int index) {
          assert isCollection();
          if (m_children == null || index >= m_children.size()) {
              return null;
          }
          return m_children.get(index);
      }
docs: Get the child member with the given index. The node must be a MAP or ARRAY. Child
  members are retained in the order they are added. If the given index is out of
  bounds, null is returned.
  
  @param   index   Zero-relative child node index.
  @return          The child member at the given index or null if there is no child
  node with the given index.