core/Request.php
public static function file(string $name = null)
    {
        if (empty($name)) {
            return $_FILES;
        }
        return isset($_FILES[$name]) ? $_FILES[$name] : null;
    }
public static function file(string $name = null)
    {
        if (empty($name)) {
            return $_FILES;
        }
        return isset($_FILES[$name]) ? $_FILES[$name] : null;
    }
获取file 相当于 $_FILE[$name]
@param string|null $name
@return null