anchor.diff:          ? null
           : new PkgResolution.fromJson(
               json['pkgResolution'] as Map<String, dynamic>),
  -    json['dartFiles'] == null
  -        ? null
  -        : new Map<String, DartFileSummary>.fromIterables(
  -            (json['dartFiles'] as Map<String, dynamic>).keys,
  -            (json['dartFiles'] as Map).values.map((e) => e == null
  -                ? null
  -                : new DartFileSummary.fromJson(e as Map<String, dynamic>))),
  +    (json['dartFiles'] as Map<String, dynamic>)?.map((k, e) => new MapEntry(
  +        k,
  +        e == null
  +            ? null
  +            : new DartFileSummary.fromJson(e as Map<String, dynamic>))),
       json['platform'] == null
           ? null
           : new DartPlatform.fromJson(json['platform'] as Map<String, dynamic>),
  
positive.code:     writeNotNull('components', components);
      writeNotNull(
          'uses',
          uses == null
              ? null
              : new Map<String, dynamic>.fromIterables(
                  uses.keys,
                  uses.values.map(
                      (e) => e == null ? null : e.toString().split('.')[1])));
      writeNotNull('reason', reason);
      return val;
    }
  
negative.code:         ?.toList(),
      json['fitness'] == null
          ? null
          : new Fitness.fromJson(json['fitness'] as Map),
      json['maintenance'] == null
          ? null
          : new Maintenance.fromJson(json['maintenance'] as Map<String, dynamic>),
  