user_id 連携で登録できない

問題は、連携したuser_idが Integrity constraint violation: 1048 Column 'user_id' cannot be nullのエラーが出ます。

laravel5.4を使っています。

登録ボタンを押すと下記のエラーが出ます、どうすれば解決できますか？

(2/2) QueryException
SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'user_id' cannot be null (SQL: insert into `jobs` (`job_id`, `user_id`, `updated_at`, `created_at`) values (2121212, , 2017-08-08 21:32:21, 2017-08-08 21:32:21))

userテーブル:
id | name |

Jobテーブル:
id | user_id | job_id

説明:
user_idはuserテーブルとjobテーブルを連携する為です
job_idはuser毎に複数のJob_idを登録したいです、使いやすい為、jobテーブルに分離しました。

UserModel:

<?php

namespace App;

use Illuminate\Notifications\Notifiable;
use Illuminate\Foundation\Auth\User as Authenticatable;


class User extends Authenticatable
{
    use Notifiable;

    /**
     * The attributes that are mass assignable.
     *
     * @var array
     */
    protected $fillable = [
        'name', 'email', 'password',
    ];

    /**
     * The attributes that should be hidden for arrays.
     *
     * @var array
     */
    protected $hidden = [
        'password', 'remember_token',
    ];

    public function jobs(){

        return $this->hasMany('App\Job');

    }
}

jobModel:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Job extends Model
{

	protected $fillable = [

	    'user_id',
	    'job_id'
	];

	public function user(){

		return $this->belongsTo('App\User');
	}

}

jobscreateRequest:

<?php

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;

class JobsCreateRequest extends FormRequest
{
    /**
     * Determine if the user is authorized to make this request.
     *
     * @return bool
     */
    public function authorize()
    {
        return true;
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return [
            'user_id' =>'required',
            'job_id'  => 'required',
        ];
    }
}

JobController:

<?php

namespace App\Http\Controllers;

use Illuminate\Support\Facades\Auth;
use App\Http\Requests\JobsCreateRequest;
use Illuminate\Http\Request;
use App\User;
use App\Job;

class UserJobsController extends Controller
{
    /**
     * Display a listing of the resource.
     *
     * @return \Illuminate\Http\Response
     */
    public function index()
    {
        $users = User::latest()->get();
        $query = Job::query();
        $jobs = $query->orderBy('created_at','desc')->paginate(5);
        return view('admin.jobs.index', compact('jobs','users'));
    }

    /**
     * Show the form for creating a new resource.
     *
     * @return \Illuminate\Http\Response
     */
    public function create()
    {
         $users = User::pluck('name','user_id');
        return view('admin.jobs.index',compact('users'));
    }

    /**
     * Store a newly created resource in storage.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return \Illuminate\Http\Response
     */
    public function store(Request $request)
    {

        $user= Auth::user();

        Job::create([
            'name' => request('name'),
            'job_id' => request('job_id'),
            'user_id' => auth()->id()
        ]);

        return redirect('/admin/jobs/index');

    }
}

index.blade.php

            <div class="col-sm-8">
                {!! Form::open(['method'=>'POST', 'action'=> 'JobsController@store']) !!}
                {{ csrf_field() }}
                     <div class="form-group">
                        {!! Form::label('user_id','名前') !!}
                        {!! Form::select('user_id[]', $users->pluck('name', 'id')->toArray(), null, ['class' => 'form-control']) !!}
                    </div> 

                    <div class="form-group">
                        {!! Form::label('job_id','Job_ID') !!}
                        {!! Form::text('job_id',null,['class'=>'form-control',]) !!}
                    </div>

                    <div class="form-group">
                        {!! Form::submit('登録', ['class'=>'btn btn-info']) !!}
                    </div>

                    @include('includes.form_error')
                {!! Form::close() !!}

            </div>