anchor.diff:    Future<Null> keepSynced(bool value) {
       return _database._channel.invokeMethod(
         'Query#keepSynced',
  -      <String, dynamic>{ 'path': path, 'parameters': _parameters, 'value': value },
  +      <String, dynamic>{
  +        'path': path,
  +        'parameters': _parameters,
  +        'value': value
  +      },
       );
     }
   }
  
positive.code:         _handle.then((int handle) async {
            await _database._channel.invokeMethod(
              'Query#removeObserver',
              <String, dynamic>{ 'handle': handle },
            );
            FirebaseDatabase._observers.remove(handle);
          });
  
negative.code:   /// [equalTo].
    Query orderByKey() {
      assert(!_parameters.containsKey('orderBy'));
      return _copyWithParameters(<String, dynamic>{'orderBy': 'key'});
    }
  
    /// Generate a view of the data sorted by value.
  