CODEWITHSUNDEEP
flutterdartflutter-dependenciesflutter-providerdart-null-safety
xpetta
xpetta

Reputation: 718

Getting an error "Null check operator used on a null value" when trying to consume value from provider

I'm getting the below error when trying to execute my flutter app:

======== Exception caught by widgets library =======================================================
The following _CastError was thrown building VerifyEmail(dirty, dependencies: [_InheritedProviderScope<User?>], state: _VerifyEmailState#da862):
Null check operator used on a null value

The relevant error-causing widget was: 
  VerifyEmail file:///Users/sas/Projects/Development/App/Flutter/netapp/lib/screens/sign_up.dart:152:61
When the exception was thrown, this was the stack: 
#0      _VerifyEmailState.build (package:netapp/screens/verify_email.dart:58:40)
#1      StatefulElement.build (package:flutter/src/widgets/framework.dart:4691:27)
#2      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4574:15)
#3      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4746:11)
#4      Element.rebuild (package:flutter/src/widgets/framework.dart:4267:5)
...
====================================================================================================

The error causing code:

    User? firebaseUser = Provider.of<User?>(context, listen: false);
    String? emailAddress = firebaseUser!.email;

If I do not specify the null check operator [!] to email then I get a syntax error.

I'm using this emailAddress variable within a Text widget.

                Text(
                  emailAddress!,
                  textAlign: TextAlign.center,
                  style: GoogleFonts.roboto(
                    textStyle: Theme.of(context).textTheme.subtitle1!.copyWith(
                          color: kBrandAccentColor,
                        ),
                  ),
                ),

The code listed below is relevant to the provider present within the main.dart file:

    return MultiProvider(
      providers: [
        StreamProvider<User?>.value(
          value: AuthService().onAuthStateChanged,
          initialData: null,
        ),
       ]
      )

The below code is present within my authentication service file:

  Stream<User?> get onAuthStateChanged => authInstance.authStateChanges();

Versions of the packages:

  firebase_core: ^1.3.0
  firebase_auth: ^1.4.1
  cloud_firestore: ^2.2.2
  provider: ^5.0.0

Output of the flutter --version:

Flutter 2.2.1 • channel stable • https://github.com/flutter/flutter.git
Framework • revision 02c026b03c (5 weeks ago) • 2021-05-27 12:24:44 -0700
Engine • revision 0fdb562ac8
Tools • Dart 2.13.1

Upvotes: 0

Views: 474

Answers (1)

dumazy
dumazy

Reputation: 14445

The firebaseUser is still null when you want to ask its email. By using the ! operator, you explicitly tell "I personally guarantee this object is not null", which isn't the case so it throws the exception.

Maybe you wanted to use the ? operator instead?

String? emailAddress = firebaseUser?.email;

This will use optional chaining, which seems to be the thing you need here.

Upvotes: 1

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