Adding creating by and updated by to TO-DO list

I am working on a to-do application, and I figured out how to add the logged in user's id to a new data they created, so you can see who created the task, but I would like to also see who updated it. My basic idea would be, to refer to the user id in the migrations both in the case of created_by and updated_by, but then when you create a new task, I get an error message that of course I didn't put any value for my updated_by. This is the first time for me doing this, so I'm kinda confused.

Migrations:

<?php

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

class CreateTasksTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('tasks', function (Blueprint $table) {
            $table->id();
            $table->string("title");
            $table->string("description");
            $table->bigInteger("created_by")->unsigned();
            $table->foreign("created_by")->references("id")->on("users")->onDelete("cascade");
            $table->bigInteger("updated_by")->unsigned();
            $table->foreign("updated_by")->references("id")->on("users")->onDelete("cascade");
            $table->timestamps();
        });
    }

TaskController:

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use Illuminate\Support\Facades\Auth;
use App\Task;

class TaskController extends Controller
{
    /**
     * Display a listing of the resource.
     *
     * @return \Illuminate\Http\Response
     */
    public function index()
    {
        $tasks = Task::all();
        $user = Auth::user();

     return view('tasks/index', compact('tasks','user'));
    }

    /**
     * Show the form for creating a new resource.
     *
     * @return \Illuminate\Http\Response
     */
    public function create()
    {
        return view('tasks/create');
    }

    /**
     * Store a newly created resource in storage.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return \Illuminate\Http\Response
     */
    public function store(Request $request)
    {
        $this->validate($request, [
            'title' => 'required|max:255',
            'description' => 'required|max:350'
        ]);
        $task = new Task();
        $task->title = $request->title;
    	$task->description = $request->description;
    	$task->created_by = Auth::id();
    	$task->save();
   
        return redirect('/tasks')->with('success', 'Aufgabe wurde erfolgreich hinzugefügt!');
    }

    /**
     * Display the specified resource.
     *
     * @param  int  $id
     * @return \Illuminate\Http\Response
     */
    public function show($id)
    {
        $task = Task::findOrFail($id);

        return view('tasks/show', compact('task'));
    }

    /**
     * Show the form for editing the specified resource.
     *
     * @param  int  $id
     * @return \Illuminate\Http\Response
     */
    public function edit($id)
    {
        $task = Task::findOrFail($id);

     return view('tasks/edit', compact('task'));
    }

    /**
     * Update the specified resource in storage.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  int  $id
     * @return \Illuminate\Http\Response
     */
    public function update(Request $request, Task $task)
    {
        $this->validate($request, [
            'title' => 'required|max:255',
            'description' => 'required|max:350'
        ]);
        $task->title = $request->title;
        $task->description = $request->description;
        $task->updated_by = Auth::id();
    	$task->save();
   

        return redirect('/tasks')->with('success', 'Aufgabe wurde erfolgreich bearbeitet!');
    }

    /**
     * Remove the specified resource from storage.
     *
     * @param  int  $id
     * @return \Illuminate\Http\Response
     */
    public function destroy($id)
    {
        $task = Task::findOrFail($id);
        $task->delete();

        return redirect('/tasks')->with('success', 'Aufgabe wurde erfolgreich gelöscht!');
    }
}