PHP：laravel 获取输入的空字符串

<?php
class Kernel extends HttpKernel
{
    protected $middleware = [
        // \App\Http\Middleware\TrustHosts::class,
        \App\Http\Middleware\TrustProxies::class,
        \Illuminate\Http\Middleware\HandleCors::class,
        \App\Http\Middleware\PreventRequestsDuringMaintenance::class,
        \Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,
        \App\Http\Middleware\TrimStrings::class,
        // bug: 空字符串转为了null
        // \Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,
    ];