SQLSTATE [23000]: Integrity constraint violation: 19 NOT NULL constraint failed: in laravel

i having a problem can find a solution on their own.

I want to do for a model in i form, but i keep getting this error

SQLSTATE [23000]: Integrity constraint violation: 19 NOT NULL failure: drivers.user_id (SQL: insert into "drivers" ("vehicle_color", "plate_number", "join_date", "updated_at", "created_at") values ​​(black, T701344C, 04/16/2017, 2017-04-16 18:32:04, 2017-04-16 18:32:04))

My controller

public function store(Request $request)
{
    $this->validate($request, [
        'first_name' => 'required|max:50',
        'last_name' => 'required|max:50',
        'phone_number' => 'required|numeric|unique:users',
        'email' => 'required|email|max:255|unique:users',
        'password' => 'required|min:6|confirmed',
        'vehicle_id' => 'required',
        'vehicle_color' => 'required',
        'plate_number' => 'required',
    ]);

    $user = new User();
    $user->first_name = $request->input('first_name');
    $user->last_name = $request->input('last_name');
    $user->phone_number = $request->input('phone_number');
    $user->email = $request->input('email');
    $user->password = $request->input('password');
    $user->sex = $request->input('sex');
    $user->dob = $request->input('dob');
    if($request->hasFile('avatar')){
        $user->avatar = $request->file('avatar')->store('uploads/clients/avatar', 'public');
    }

    $user->dob = true;
    $user->verified = true;

    $user->save();

    $user->driver()->create([
        'vehicle_id' => $request->input('vehicle_id'),
        'vehicle_color' => $request->input('vehicle_color'),
        'plate_number' => $request->input('plate_number'),
        'join_date' => Carbon::now()->format('m/d/Y'),
    ]);

    $role = Role::whereName('driver')->first();
    $user->assignRole($role);

    alert()->success('Driver successfully added.')->autoclose(3000)->persistent('Close');
    return redirect()->route('backend.drivers.index');
}

      

        
        
        
      

    

in the custom structure of the custom model

public function driver()
{
    return $this->belongsTo(Driver::class);
}

      

        
        
        
      

    

in relation to the driver model

public function user()
{
    return $this->belongsTo(User::class, 'user_id');
}

      

        
        
        
      

    

Driver table

Schema::create('drivers', function (Blueprint $table) {
        $table->increments('id');
        $table->integer('all_time_job')->nullable();
        $table->string('vehicle_color')->nullable();
        $table->string('plate_number')->nullable();
        $table->date('join_date')->nullable();

        $table->integer('user_id')->unsigned()->index();
        $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');

        $table->integer('vehicle_id')->unsigned()->index();
        $table->foreign('vehicle_id')->references('id')->on('vehicles');
        $table->timestamps();
    });

      

        
        
        
      

    

Users table

Schema::create('users', function (Blueprint $table) {
        $table->increments('id');
        $table->string('first_name');
        $table->string('last_name');
        $table->string('phone_number')->unique();
        $table->string('avatar')->nullable();
        $table->string('dob')->nullable();
        $table->string('email')->unique();
        $table->string('password');
        $table->boolean('verified')->default(false);
        $table->string('token')->nullable();
        $table->rememberToken();
        $table->timestamps();
    });

      

        
        
        
      

    

Can someone help me with this

Stores user data in the user table, but does not store the driver date in the driver table.

I user laravel 5.4