The following code is login control in Flutter. Firstly I entered true user but the response is null, then I entered false login, also the response is null. What's wrong?

Future save() async {
        var res = await http.post("http://localhost:8080/signinUser",
            headers: <String, String>{
              'Context-Type': 'application/json;charSet=UTF-8'
            },
            body: <String, String>{
              'email': user.email,
              'password': user.password
            });
        print(res.body);
        if(res.body!=null){
          Navigator.push(
              context, new MaterialPageRoute(builder: (context) => Dashboard()));
        }
    
      }