Unhandled Exception: type '(dynamic) => Null' is not a subtype of type '(String, dynamic) => void' of 'f' in the Data model

Question

I am getting this Error Unhandled Exception: type \'(dynamic) => Null\' is not a subtype of type \'(String, dynamic) => void\' of \'f\' decoding a json from an API, I beli