function required(rule, value, source, errors, options, type) {
  if (rule.required && (!source.hasOwnProperty(rule.field) || __WEBPACK_IMPORTED_MODULE_0__util__["f" /* isEmptyValue */](value, type || rule.type))) {
    errors.push(__WEBPACK_IMPORTED_MODULE_0__util__["e" /* format */](options.messages.required, rule.fullField));
  }
}
Rule for validating required fields.

 @param rule The validation rule.
 @param value The value of the field on the source object.
 @param source The source object being validated.
 @param errors An array of errors that this rule may add
 validation errors to.
 @param options The validation options.
 @param options.messages The validation messages.