anchor.diff:              context['arguments'], context['pathSuffixes'], context['paths']);
         } else {
           return new shelf.Response.internalServerError(
  -            body: 'Data source does not implement the requested method');
  +            body: JSON.encode({'error': 'Data source does not implement the requested method'}));
         }
       } catch (e) {
         rethrow;
  -      return new shelf.Response.internalServerError(body: e.toString());
  +      return new shelf.Response.internalServerError(body: JSON.encode({'error': e.toString()}));
       }
   
       return new shelf.Response.ok(
  
positive.code:     Map context = await requestToContext(request);
      Router router = getDataSource(request);
  
      if (context.keys.isEmpty) {
        return new shelf.Response.internalServerError(
            body: 'Request not supported');
      }
      if (context['method'] == null || context['method'].isEmpty) {
        return new shelf.Response.internalServerError(
            body: 'No query method provided');
      }
      if (context['method'] != 'set' &&
          (context['paths'] is! List ||
              context['paths'].any((path) => path is! List))) {
        return new shelf.Response.internalServerError(
            body: 'Paths must be a set of paths');
      }
  
      try {
  
negative.code:   };
  }
  
  Future<Map> requestToContext(shelf.Request request) async {
    var queryMap = request.method == 'POST'
        ? JSON.decode(await request.readAsString())
        : Uri.parse(request.requestedUri.toString()).queryParameters;
  