Maps and Nulls

main.dart

/// MapContainer is a class that can have an optionally null map
class MapContainer{
  final Map<String, String>? map;
  MapContainer(this.map);
}

void main() {
  /// dart added support to null aware subscript operator in the NNBD features update.
  /// See: https://github.com/dart-lang/language/issues/376 
  /// See: https://nullsafety.dartpad.dev/f6866ea63dde8098f68ffd39ed944555/
  /// this way, we will be able to use something like this:
  print(MapContainer(null).map?["hello"] ?? "NA");
  
  /// In Non NNBD code, this is the best approach: 
  /// see: https://dartpad.dev/f6866ea63dde8098f68ffd39ed944555/
  /// when the map is null, we substitute it with empty and then use the subscripting operator
  print((MapContainer(null).map?? {})["hello"] ?? "NA");
  /// when the map is empty, we still get the desired results
  print((MapContainer({}).map?? {})["hello"] ?? "NA");
  /// when the map has the key, we still get the desired result.
  print((MapContainer({"hello": "world"}).map?? {})["hello"] ?? "");
}