anchor.diff:    }
   
     Map<String, dynamic> buildArguments() {
  -    return new Map<String, dynamic>.from(_parameters)..addAll(<String, dynamic>{
  -      'path': path,
  -    });
  +    return new Map<String, dynamic>.from(_parameters)
  +      ..addAll(<String, dynamic>{
  +        'path': path,
  +      });
     }
   
     Stream<Event> _observe(_EventType eventType) {
  
positive.code:         _handle.then((int handle) async {
            await _database._channel.invokeMethod(
              'Query#removeObserver',
              <String, dynamic>{ 'handle': handle },
            );
            FirebaseDatabase._observers.remove(handle);
          });
  
negative.code:     controller = new StreamController<Event>.broadcast(
        onListen: () {
          _handle = _database._channel.invokeMethod(
            'Query#observe',
            <String, dynamic>{
              'path': path,
              'parameters': _parameters,
              'eventType': eventType.toString(),
  