get method
Get value in cache or get fallback or null
Implementation
@override
Future<V?> get(K k, {V? fallback}) async {
if(exist(k)){
return _cache[k];
}
if(_futures.containsKey(k)){
final res = await _futures[k]?.call();
_cache[k] = res as V;
return res;
}
if(fallback != null){
return fallback;
}
return null;
}