operator [] method
The value for the given key, or null if key is not in the map.
Some maps allow null as a value.
For those maps, a lookup using this operator cannot distinguish between a
key not being in the map, and the key being there with a null value.
Methods like containsKey or putIfAbsent can be used if the distinction
is important.
Implementation
@override
RecursiveMap? operator [](Object? key) {
if (_map.containsKey(key)) {
return _map[key] ?? RecursiveMap();
}
return null;
}