sign in The method '_mulFromInteger' was called on null

Question

I've got sign in methode in my provider.

  Future<void> signIn(
      String email, String password, BuildContext context) async {
    SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
    final clientID = "com.super.app";
    final body = "username=$email&password=$password&grant_type=password";
    final String clientCredentials =
        const Base64Encoder().convert("$clientID:".codeUnits);

    try {
      final http.Response response =
          await http.post("http://localhost:8888/auth",
              headers: {
                "Content-Type": "application/x-www-form-urlencoded",
                "Authorization": "Basic $clientCredentials"
              },
              body: body);
      final jsonResponse = json.decode(response.body);
//      if (jsonResponse["error"] != null) {
//        throw HttpException(jsonResponse["error"]);
//      }
      _userId = 1;
      _token = jsonResponse['access_token'];
      _expiryDate = DateTime.now().add(
        Duration(
          seconds: jsonResponse['expires_in'],
        ),
      );
      _autoLogout();
      notifyListeners();
      final userData = json.encode(
        {
          'userId': 1,
          'email': email,
          'token': _token,
          'expiryDate': _expiryDate.toIso8601String(),
        },
      );
      sharedPreferences.setString('userData', userData);
    } catch (error) {
      print(error.toString()); //<-- misleading error
    }
  }

All works fine but when incorrect login credential are passed then I get misleading error

flutter: NoSuchMethodError: The method '_mulFromInteger' was called on null.
Receiver: null
Tried calling: _mulFromInteger(1000000)

The back end passing error code 400 and body {"error": "invalid client"} but I get that strange error as output. So what does that error means and why do I get that instead of body

Solution

As from @Suragch comments I had few problem in my code. First I thought that when server return 400 code then it will automatically throw an error and skip rest of the lines.. I was wrong so basically I had to uncomment my code for http exceptions and in my button catch the error

  try {
    await Provider.of<Auth>(context, listen: false).signIn(
        emailController.text, passwordController.text);
  } on HttpException catch (error) {
    print(error.toString());
  } catch (error) {
    print(error);
  }

Comments

[Haidar]

can you provide more details, where is the error happening, in the try or catch block?

[delmin]

@LoVe it is in the catch block... commented in the code

[Haidar]

stackoverflow.com/questions/52549620/… may help clarify where the problem is coming from, also, try print(error) just to see if it can print something without giving an error

[delmin]

@LoVe That link doesn't really help in this situation and print(error) prints the same error

[Suragch]

I would try to pear down the code until you isolate exactly where the error it getting thrown. Removing try/catch might help with that. I think the link that LoVe provided might actually be on the right track. There is a comment there about a null Duration causing such an error and you also have a Duration. Additionally, check the response status code before you try to do something with the response body. If the status code is 400 then there is no use trying to extract a non-existent access token.

[Suragch]

Side note: client apps probably don't need to worry about the userId. Let the server worry about that. The client only needs to worry about the email, password, and access token.

[delmin]

@Suragch I've seen that comment and absolutely forgot about the Duration in my code.. Yes that might be the case of the issue. However I thought that try block will skip everything once response from http throw an error

[Suragch]

http doesn't throw an error just because the server returns a 400 or 500 code.

[delmin]

@Suragch I see... to be honest I tried also to fix it as you can see in updated code (commented) but I get an error Unhandled Exception: Failed assertion: boolean expression must not be null So basically I can get rid of the try-catch block and simply use if else statement.. if response has error in the body throw error else continue

[Suragch]

I think what you meant to write is this: jsonResponse["error"] != null. I would still check response.statusCode rather than testing for null, though.

[delmin]

@Suragch You're right. I just noticed that silly mistake ...All fixed and working as it should

[Suragch]

Great. Consider adding your own answer below so that others who come here can benefit.

[delmin]

@Suragch Please you do it so I can at least give you some points for your help

[Suragch]

@delmin, I don't need the points. :) Besides, I prefer to answer questions with a single topic. This has two or three different issues.

[delmin]

@Suragch you're right.. I'll do it then... Sorry for that :)