code: function (identifier, field, values) {
              var self = this;
              return this.needByIdentifier(identifier).then(function (record) {
                  return self.addFieldIfNotExistById(record.id, field, values);
              });
          }
docs: Using an id, find document and update fields only if they don't exist.
  Returns a waterline (bluebird) promise with the document find and modify.
  
  @param {string} id
  @param {String} field
  @param {*} values
  @returns {Promise}