How to solved in Laravel relations null value

Im tru to use to last version of laravel and i have small problem with Laravel relationship One to Many Im try to connect products with categories

This is my code of Product model

public function categories()
{
    return $this->belongsTo('App\Category');
}

this is my code of Category model

public function products()
{
    return $this->hasMany('App\Product');
}

This is my code in controller

$products = Product::with('categories')->get();
    dd($products);

this is my code from migration files

Schema::create('products', function (Blueprint $table) {
        $table->id();
        $table->unsignedBigInteger('category_id');
        $table->string('name')->unique();
        $table->string('slug')->unique();
        $table->string('keywords')->nullable();
        $table->string('price');
        $table->text('description')->nullable();
        $table->text('image')->nullable();
        $table->timestamps();
        $table->foreign('category_id')->references('id')->on('categories');
    });

Schema::create('categories', function (Blueprint $table) {
        $table->id();
        $table->string('name')->unique();
        $table->string('slug')->unique();
        $table->string('keywords')->nullable();
        $table->timestamps();
    });[![enter image description here][1]][1]

If someone know how to solved this problem I'll be very grateful

via Chebli Mohamed