enqueue method Null safety

Future enqueue(
  1. Operation operation
)

Implementation

Future enqueue(Operation operation) {
  _queue.add(operation);
  final completer = Completer();
  _completers[operation.hashCode] = completer;

  if (!_scheduled) {
    _scheduled = true;
    Timer(Duration(seconds: 0), _execute);
  }

  return completer.future;
}