fetchSingle returning mixed, how to approach?

[dakorpar]

How to properly solve those?
I know it will allways be ?int, but since fetchSingle is marked as returning mixed I can't solve this. I wouldn't want to just skip those checks....

	public function getIdByKey(string $key): ?int
	{
		return $this->db->select('id')->from($this->table)->where('%n = %s', 'key', $key)->fetchSingle();
	}

ofcours, here is integer in some other query will be something else...

only thing I think off as correct would maybe be:

	public function getIdByKey(string $key): ?int
	{
		/** @var int|null $id */
		$id = $this->db->select('id')->from($this->table)->where('%n = %s', 'key', $key)->fetchSingle();
	}