code: protected boolean isLeaf() {
  
          for (int i = 0; i < entries.length; i++) {
              Entry entry = entries[i];
              if (entry.getChild() != null) {
                  return false;
              }
          }
  
          return true;
      }
docs: Checks if this node is a leaf. A node is a leaf when none of the entries
  in the node have children.
  @return <code>true</code> if the node is leaf, <code>false</code>
  otherwise.