code: public ClusteringFeature findLeaf(NumberVector nv) {
      if(root == null) {
        throw new IllegalStateException("CFTree not yet built.");
      }
      return findLeaf(root, nv);
    }
docs: Find the leaf of a cluster, to get the final cluster assignment.
  <p>
  In contrast to {@link #insert}, this does not modify the tree.
  
  @param nv Object data
  @return Leaf this vector should be assigned to