PHP Error in Laravel while inserting data via sqlite

I'm studying Laravel and working around in php artisan but I keep on getting this error:

Illuminate/Database/QueryException with message 'SQLSTATE[23000]: Integrity constraint violation: 19 NOT NULL constraint failed: profiles.url (SQL: insert into "profiles" ("title", "description", "user_id", "updated_at", "created_at") values (Cool, Desc, 1, 2020-03-12 02:03:16, 2020-03-12 02:03:16))'

I am attaching a Profile to a User and my User table has contents:

>> User::all()
=> Illuminate\Database\Eloquent\Collection {#2992
     all: [
       App\User {#2993
         id: "1",
         name: "Test User1",
         email: "[email protected]",
         username: "test1",
         email_verified_at: null,
         created_at: "2020-03-12 02:01:08",
         updated_at: "2020-03-12 02:01:08",
       },
     ],    }

This is what I entered in PHP Artisan

>>> $profile = new \App\Profile();
=> App\Profile {#2987}
>>> $profile->title = 'Cool Title';
=> "Cool Title"
>>> $profile->description = 'Desc';
=> "Desc"
>>> $profile->user_id = 1;
=> 1
>>> $profile->save();

Profiles_table.php

class CreateProfilesTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('profiles', function (Blueprint $table) {
            $table->bigIncrements('id')->nullable;
            $table->unsignedBigInteger('user_id')->nullable;
            $table->string('title')->nullable;
            $table->text('description')->nullable;
            $table->string('url')->nullable;
            $table->timestamps();

            $table->index('user_id');
        });
    }

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

}

Create_users_table.php

class CreateUsersTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('users', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->string('name')->nullable();
            $table->string('email')->unique();
            $table->string('username')->unique();
            $table->timestamp('email_verified_at')->nullable();
            $table->string('password')->nullable();
            $table->rememberToken()->nullable();
            $table->timestamps();
        });
    }

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

I can't find the reason why it is failing. Hope someone can find out what is causing it. Thanks