function _parseArguments(options, callback) {
  /* istanbul ignore else */
  if (typeof options === 'function') {
    return [{}, options];
  }

  /* istanbul ignore else */
  if (_isUndefined(options)) {
    return [{}, callback];
  }

  // copy options so we do not leak the changes we make internally
  const actualOptions = {};
  for (const key of Object.getOwnPropertyNames(options)) {
    actualOptions[key] = options[key];
  }

  return [actualOptions, callback];
}
Parses the function arguments.

This function helps to have optional arguments.

@param {(Options|null|undefined|Function)} options
@param {?Function} callback
@returns {Array} parsed arguments
@private