public function has_in_wishlist( $course_id = 0, $user_id = 0 ) {
		if ( ! $course_id || ! $user_id ) {
			return false;
		}

		$courses_in_wishlist = (array) get_user_meta( $user_id, '_dozent_course_wishlist' );

		return in_array( $course_id, $courses_in_wishlist );
	}