docs: function (params, cb) {
                    // validate input requirements vs what came back in params
                    var errorMessage = null;
  
                    _.forEach(Card.inputs, function (input, key) {
                      if (input.required && !params[key]) {
                        if (!errorMessage) {
                          errorMessage = '';
                        }
                        else {
                          errorMessage += ' | ';
                        }
  
                        errorMessage += 'No value provided for required input: ' + key;
                      }
                    });
  
                    cb(errorMessage, params);
                  }