error = function error(errorType) {
        var delegate = _this.delegate();
        if (delegate) {
          if (typeof delegate.textFieldDidFailToValidateChange === 'function') {
            delegate.textFieldDidFailToValidateChange(_this, change, errorType);
          }
        }
      }
Builds a change instance and formats the change to see if it's valid

@param   {object} current
@param   {object} proposed
@returns {?object} false if change doesn't have changes or change isn't valid. Change object if it is.