type 'Null' is not a subtype of type 'String' while receiving json data in flutter

Question

I am receiving photos as - "photos":[null], in my json data. (It is a list of string of urls). And in my model class, I am receiving my data as -

photos: List<String>.from(
   json["photos"].map(
         (x) => x,
   ),
),

And in my class, I tried to declare photos variable like this -

List<String?>? photos;

How should I correct this?