laravelで 1364 Field 'id' doesn't have a default valueエラーの解決方法が知りたい

前提・実現したいこと

自己学習にてLaravelでfactoryを使いデータを一旦作ろうとしているのですが、以下のエラー分が表示されてしまっている状態です。
いまいち解決方法がわからず教えていただけると助かります。
fackerなど適当一旦に設定しているのでもしその辺も修正した方がよければ言っていただけるとありがたいです。

発生している問題・エラーメッセージ

tinkerにて

factory(App\Model\ProductVariationStock::class)->make();

を実行した時に発生しているエラーです

Illuminate/Database/QueryException with message 'SQLSTATE[HY000]: General error: 1364 Field 'id' doesn't have a default value (SQL: insert into `product_variations` (`product_id`, `sku_code`, `price`, `released_at`, `expired_at`, `sale_start_at`, `sale_end_at`, `sale_lower_limit`, `sale_upper_limit`, `registered_at`, `expected_shipping_id`, `updated_at`, `created_at`) values (21, 6, 21825, 2020-05-19 00:00:00, 2020-05-21 00:00:00, 2020-05-19 00:00:00, 2020-05-21 00:00:00, 1, 20, 2020-05-20 00:00:00, 3, 2020-05-20 16:09:32, 2020-05-20 16:09:32))'

該当のソースコード

<?php

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

class CreateProductVariationsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('product_variations', function (Blueprint $table) {
            $table->bigIncrements('id')->comment('ID');
            $table->unsignedBigInteger('product_id')->comment('商品情報ID');
            $table->string('sku_code')->comment('コード');
            $table->decimal('price', 12, 2)->default(0)->comment('価格');
            $table->timestamp('released_at')->comment('公開開始日時');
            $table->timestamp('expired_at')->comment('公開終了日時');
            $table->timestamp('sale_start_at')->comment('販売開始日時');
            $table->timestamp('sale_end_at')->comment('販売終了日時');
            $table->unsignedSmallInteger('sale_lower_limit')->default(0)->comment('最小注文数');
            $table->unsignedSmallInteger('sale_upper_limit')->default(65535)->comment('最大注文可能数');
            $table->timestamp('registered_at')->default(DB::raw('CURRENT_TIMESTAMP'))->comment('商品登録日時');
            $table->unsignedBigInteger('expected_shipping_id')->comment('配送予定日ID');
            $table->softDeletes();

            $table->foreign('product_id')->references('id')->on('products');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('product_variations');
    }
}

<?php

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

class CreateProductVariationStocksTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('product_variation_stocks', function (Blueprint $table) {
            $table->bigIncrements('id')->comment('ID');
            $table->unsignedBigInteger('product_variation_id')->comment('商品バリエーションID');
            $table->unsignedSmallInteger('quantity')->comment('在庫数');

            $table->foreign('product_variation_id')->references('id')->on('product_variations');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('product_variation_stocks');
    }
}


<?php

/** @var \Illuminate\Database\Eloquent\Factory $factory */

use Carbon\Carbon;
use App\Model\Product;
use Faker\Generator as Faker;
use App\Model\ProductVariation;

$factory->define(
    ProductVariation::class,
    function (Faker $faker) {

        return [
            'product_id' => function () {
                return factory(Product::class)->create()->id;
            },
            'sku_code' => $faker->randomDigit,
            'price' => $faker->numberBetween(100, 100000),
            'released_at' => Carbon::yesterday(),
            'expired_at' => Carbon::tomorrow(),
            'sale_start_at' => Carbon::yesterday(),
            'sale_end_at' => Carbon::tomorrow(),
            'sale_lower_limit' => 1,
            'sale_upper_limit' => rand(2, 99),
            'registered_at' => Carbon::today(),
            'expected_shipping_id' => $faker->randomDigit,
        ];
    }
);