public function setSafe($options)
    {
        if (is_string($options)) {
            $this->safe[] = $options;
            return $this;
        }

        if (is_array($options)) {
            foreach ($options as $key => $value) {
                $this->safe[] = $value;
            }
            return $this;
        }

        throw new InvalidArgumentException(
            'This method expects a string or an array argument.'
        );
    }