code: @Override
  	public TreeNode<T> getChild(final int index) {
  		if (_children == null) {
  			throw new ArrayIndexOutOfBoundsException(format(
  				"Child index is out of bounds: %s", index
  			));
  		}
  
  		return _children.get(index);
  	}
docs: Returns the child at the specified index in this node's child array.
  
  @param index   an index into this node's child array
  @return the tree-node in this node's child array at the specified index
  @throws ArrayIndexOutOfBoundsException  if the {@code index} is out of
  bounds