result.dart

GraphQLClient _client = graphQLConfiguration.clientToQuery();
    QueryResult result = await _client.mutate(
      MutationOptions(
        document: addMutation.register('$_email','','$_password'),
      ),
    );
    if (result.data["success"]!=null){
      print('The user was created successfully!');
    }else{
      print('There was an error!');
      print(result.data["register"]["errors"]["email"][0]["message"]);
    }