sfp_api_laravel_ginastica_cerebro/app/Http/Middleware/ConvertStringNullToNull.php

<?php

namespace App\Http\Middleware;

use Illuminate\Foundation\Http\Middleware\TransformsRequest;

class ConvertStringNullToNull extends TransformsRequest
{
    /**
     * Transform the given value.
     *
     * @param  string  $key
     * @param  mixed  $value
     * @return mixed
     */
    protected function transform($key, $value)
    {
        return $value === 'null' ? null : $value;
    }
}