function dozent_attached_product_type_to_course( $course = null ) {
		if ( ! $course ) {
			return null;
		}

		$course     = dozent_get_course( $course );
		$product_id = dozent_get_attached_product_id_by_course( $course->get_id() );
		$product_type = false;

		if ( $course->is_closed() && $product_id ) {
			$product_type = get_post_meta( $course->get_id(),'_product_by', true );

			//Check rest of other integration
		}

		return apply_filters( 'dozent_attached_product_type_to_course', $product_type, $course );
	}