Timestamps in Laravel 5.2.7 have default null values

I'm using Laravel Framework version 5.2.7. I created a database migration as shown below:

<?php

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateLessonsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('lessons', function (Blueprint $table) {
            $table->increments('id');
            $table->string('title');
            $table->text('body');
            $table->boolean('some_bool');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::drop('lessons');
    }
}

I went in the virtual machine's MySql database and used the command desc lessons;, this is what I'm getting:

I don't understand why do created_at and updated_at columns have NULL as the Default. I went to Laravel 5.2 documentation and saw this:

$table->timestamps(); Adds created_at and updated_at columns. $table->nullableTimestamps(); Same as timestamps(), except allows NULLs.

So according to the documentation $table->timestamps() should not allow NULL as default. But still I'm getting created_at and updated_at columns having NULL as the default. Why is this?

In fact these columns should be like this table:

If you use $table->timestamp('created_at') instead of $table-timestamps() in your schema builder, default value will be CURRENT_TIMESTAMP and it won't be NULL.

Likewise to store update time of a record: $table->timestamp('updated_at').

The difference is in just a letter 's' and have to mention the column name such as created_at/created, updated_at/updated.