Convert null value from database to empty string for response

NullToEmptyString.php

<?php
namespace App\Traits;

/**
 * Convert null value from database to empty string for response
 * 
 * Usage:
 * use Illuminate\Database\Eloquent\Model;
 * use App\Traits\NullToEmptyString;
 *
 * class Order extends Model
 * {
 *   use NullToEmptyString;
 * 
 *   ....
 * }
 */
trait NullToEmptyString 
{
    public static function bootNullToEmptyString()
    {
        static::retrieved(function($model) {
            foreach ((array) $model->fillable as $key) {
                if ($model->getAttribute($key) === null) {
                    $model->attributes[$key] = '';
                }
            }
        });
    }
}