Flutter: Fix "Argument type 'String' can't be assigned to 'List<dynamic>

I'm encountering the following error in my Flutter project:

 The argument type 'String' can't be assigned to the parameter type
 'List<dynamic>'.

This error appears within this code:

import 'package:flutter/material.dart';
// ... other imports 

class MainController extends StatefulWidget {
  // ... existing code 
}

class Functionality extends State<MainController> {
  String _userName; // Likely source of the problem
  int userPoints = 0;
  Authenticate authenticate;

  // .. existing code

  Widget sideMenu(String titleName, IconData takeIcon) {
    // ... existing code 

    if (titleName == "Account") {
      List? takeInformation = authenticate.fetchDataToPreview(this._userName); 
      Navigator.push(
          context,
          MaterialPageRoute(
              builder: (context) =>
                  AccountInformation(this._userName, takeInformation!))); // Potential null issue
    } 
    // ... rest of the function 
  }

  // ... rest of the code 
}

Things I've tried:

• I tried final String _userName but no luck, in this line:

  String _userName;
  

• Added "!" to takeInformation in the Navigator.push line, but the error persists

   AccountInformation(this._userName, takeInformation!)));
  

Questions:

1. How can I ensure that authenticate.fetchDataToPreview() indeed returns a List<dynamic>? Could there be a type mismatch causing this error?
2. Is there an issue with how I'm handling potential null values in the takeInformation list?

Additional Context

• I'm using Flutter with Android Studio.

in AccountInformation class, I guess you defined your user name as List like this:

final List username;

if you want to pass username as string type change it to:

final String username;