Laravel resource return null or db value

I need help, I want assistance with my api, I want to return an image if its available on the database or return null if no value on db.

Th is is my resource code

 return [
             'id'    => $this->id,
            'name' => $this->name,
            'photo' => isset($this->photo) ? url('/storage',$this->photo) : "",
        ];

Here is my json that is returns

"data": [
        {
            "id": 1,
            "name": "Public Safety",
            "photo": "https://xxxxxxxxxxxxx/storage"
        },
        {
            "id": 2,
            "name": "Severe / Extreme Weather",
            "photo": "https://xxxxxxxxxxxxx/storage"
        },

I want it to return photo data only if there is a value on db column, if nothing is there then return null.

via Chebli Mohamed