private static void verifyProperty1(RBTreeNode<?, ?> node) {
        //Check ourselves
        assert nodeColor(node) == Color.RED || nodeColor(node) == Color.BLACK;
        //If we're not null, check our (potential) children
        if (node == null) return;
        //Null children will read as black, due to how tree is defined (specifically nodeColor)
        verifyProperty1(node.left);
        verifyProperty1(node.right);
    }