laravel 怎么更改表结构

php artisan make:migration add_images_to_articles_table --table=articles

Created Migration: 2018_03_21_225819_add_images_to_articles_table

database/migrations/2018_03_21_225819_add_images_to_articles_table.php

public function up()
{
Schema::table('articles', function (Blueprint $table) {
$table->text('images');
});
}

php artisan migrate

Migrating: 2018_03_21_225819_add_images_to_articles_table
Migrated:  2018_03_21_225819_add_images_to_articles_table

**************************************
*     Application In Production!     *
**************************************
 Do you really wish to run this command? (yes/no) [no]:
 > yes
Migrating: 2018_03_21_225819_add_images_to_articles_table
Migrated:  2018_03_21_225819_add_images_to_articles_table

SQLSTATE[HY000]: General error: 1364 Field 'images' doesn't have a default value

$table->text('images')->nullable()->change();