code: function checkArray(obj, key, fallback) {
  
      /* istanbul ignore if */
      if (Object.prototype.hasOwnProperty.call(obj, key) && !Array.isArray(obj[key])) {
          throw new TypeError(`${key}, if provided, must be an Array`);
      }
      return obj[key] || fallback;
  }
docs: Ensure that if the key is provided, it must be an array.
  @param {Object} obj Object to check with `key`.
  @param {string} key Object key to check on `obj`.
  @param {*} fallback If obj[key] is not present, this will be returned.
  @returns {string[]} Returns obj[key] if it's an Array, otherwise `fallback`