anchor.diff:        }, onError: (error, stackTrace) {
           output.addError(error, stackTrace);
         });
  -    }).catchError((error, stackTrace) {
  +    })
  +    .catchError((error, stackTrace) {
         final response = new shelf.Response.internalServerError(
             body: '{"error":"internal_server_error",'
             ' "message": "I couldn\'t connect to the database. Contact your database administrator."}',
  
positive.code: 
    Future _ensureHasValidated() {
      if (hasValidated) return new Future.value();
      _validateSession().then((_) {
        final interval = new Duration(minutes: 9);
        new Timer.periodic(interval, (_) => _validateSession());
      });
  
negative.code:         pathSegments: uri.pathSegments,
          queryParameters: uri.queryParameters,
          fragment: uri.fragment);
      _ensureHasValidated()
      .then((_) => client.openUrl(method, couchUri))
      .then((HttpClientRequest request) {
        for (var header in headers.keys) {
          request.headers.add(header, headers[header]);
        }
  