containsKeyNoPurge method
Returns true if key has an associated value.
Same as containsKey, but does NOT purge entries whose key or value has already been collected.
Implementation
bool containsKeyNoPurge(Object? key) {
if (key == null || key is! K) return false;
var k = _EntryKey<K, V>(key);
// ignore: collection_methods_unrelated_type
return _map.containsKey(k);
}