List returnMovies = [];

Future<List> _getData() async {

    final response = await http.get("https:../getTodayMovies",
        headers: {HttpHeaders.AUTHORIZATION: Acess_Token.access_token});


    if (response.body != null) {
    returnMovies = json.decode(response.body);
      .....

      setState(() {});
    } else {
       final responseUpcoming = await http.get("/upcoming",
        headers: {HttpHeaders.AUTHORIZATION: Acess_Token.access_token});
        returnMovies = json.decode(returnUpcoming.body);


    }

returnMovies.addAll(json.decode(returnUpcoming.body))