php 验证所传参数为必填的时候的验证逻辑

此段代码摘自lumen框架： xx/vendor/illuminate/validation/Validator.php
/**
     * Validate that a required attribute exists.
     *
     * @param  string  $attribute
     * @param  mixed   $value
     * @return bool
     */
    protected function validateRequired($attribute, $value)
    {
        if (is_null($value)) {
            return false;
        } elseif (is_string($value) && trim($value) === '') {
            return false;
        } elseif ((is_array($value) || $value instanceof Countable) && count($value) < 1) {
            return false;
        } elseif ($value instanceof File) {
            return (string) $value->getPath() != '';
        }

        return true;
    }