default T lastLeaf() {
		T leaf = self();
		while (!leaf.isLeaf()) {
			leaf = leaf.lastChild().orElseThrow(AssertionError::new);
		}

		return leaf;
	}
Return the last leaf that is a descendant of this node; either
{@code this} node or its last child's last leaf. Returns {@code this}
node if it is a leaf.

@see #isLeaf
@see #isDescendant
@return the last leaf in this subtree
jenetics.ext/src/main/java/io/jenetics/ext/util/Tree.java