Attempt to read property title on null Laravel

Hi,

I’m getting this error:

Attempt to read property [title] on null

This my relationship in my model:

public function ad_types()
{
return $this->belongsTo(AdType::class);
}

This is how I’m trying to output it in my blade view:

{{ $ad->ad_types->title }}

Here is my migration file:

Schema::create('ads', function (Blueprint $table) {
$table->bigIncrements('id');
$table->string('title', 191)->unique();
$table->string('ad_url', 191);
$table->string('ad_img')->nullable();
$table->unsignedBigInteger('ad_type_id')->default(1);
$table->foreign('ad_type_id')->references('id')->on('ad_types');
$table->timestamps();
});

What am I doing wrong?

Thanks