41      * @param mixed $offset
45     public function offsetExists($offset): bool {  argument
46         return isset($this->nodes[$offset]);
52      * @param mixed $offset
57     public function offsetGet($offset) {  argument
58         return isset($this->nodes[$offset]) ? $this->nodes[$offset] : null;
64      * @param mixed $offset
67     public function offsetSet($offset, $value): void {  argument
68         if (is_null($offset)) {
71             $this->nodes[$offset] = $value;
78      * @param mixed $offset
80     public function offsetUnset($offset): void {  argument
81         unset($this->nodes[$offset]);