anchor.diff:    if (obj is List) {
       List<Object> list = new List<Object>();
       for (var e in obj) {
  -      list.add(_serialize(e));
  +      list.add(_serializeObject(e));
       }
       return list;
     }
  
positive.code: library json_mapper;
  
  import 'dart:mirrors' as mirrors;
  
  /**
   * Serializes the provided [obj] into a valid JSON [String].
  
negative.code:   if (obj is Map) {
      // what if key is not string?
      for (var k in obj.keys) {
        data[k] = _serializeObject(obj[k]);
      }
      return data;
    }
  