public long getLast() {
        if (root == null) {
            return -1;
        }
        RBNode node = root;

        while(node.right != null) {
            node = node.right;
        }
        return node.key;

    }
Returns the last key in this set.
Ghidra/Framework/Generic/src/main/java/ghidra/util/datastruct/RedBlackLongKeySet.java