Method _createCheckThatThrows

packages/helpers/classes/mail.js:647–653

* Create a check out of a callback. If the callback * returns false, the check will throw an error.

(check, errorString)

   * returns false, the check will throw an error.
   */
  _createCheckThatThrows(check, errorString) {
    return (propertyName, value) => {
      if (!check(value)) {
        throw new Error(errorString);
      }
    };
  }

  /**
   * Set an array property after checking that the new value is an