public function __construct(?string $model, ?string $field_name, ?string $market_id, ?string $field_value, ?string $id) 	{ 		$this->field_name = $field_name ?? 'sku'; 		$this->market_id = $market_id ?? ''; 		$this->field_value = $field_value ?? ''; 		$this->model = $model ?? Product::class; 		$this->id = $id; 	}