docs: function(className, params, callback) {
          /**
           * Callback for QB.data.uploadFile(className, params, callback)
           * @callback uploadFileToDataCallback
           * @param {object} error - The error object
           * @param {object} response - The file object
           */
          var data = {
                  field_name: params.field_name,
                  file: {
                      data: params.file,
                      name: params.name
                  }
              };
  
          this.service.ajax({
              'url': Utils.getUrl(config.urls.data, className + '/' + params.id + '/file'),
              'type': 'POST',
              'fileToCustomObject': true,
              'contentType': false,
              'data': data,
          }, function(err, result){
              if (err) {
                  callback(err, null);
              } else {
                  callback (err, result);
              }
          });
      }