Can a button be shown based on an optional void function in Flutter?

I have a class where I declare an optional void function as parameter for the constructor of that class.
If the parameter (that optional void function) is not null I want to show a button.
On my second class I call the constructor and I pass a function to that optional parameter.
The problem is that my button never shows up on the screen and I don’t know what I’m doing wrong.
Can someone please help me to figure out where is the issue in my code ?

Here is my code:

import 'package:flutter/material.dart';

class Login extends StatefulWidget {
  final Function(void)?
      showCreateAccountBtn; // This parameter is optional and represent a void function.
  const Login({
    Key? key,
    this.showCreateAccountBtn,
  }) : super(key: key);

  @override
  State<Login> createState() => _LoginState();
}

class _LoginState extends State<Login> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: const Text("First Screen")
        ),
        body: Column(children: [
          widget.showCreateAccountBtn != null
              ? TextButton(
                  style: ButtonStyle(
                      foregroundColor:
                          MaterialStateProperty.all<Color>(Colors.blue)),
                  onPressed: () => widget.showCreateAccountBtn,
                  child: const Text('Create an account'))
              : const SizedBox()
        ]));
  }
}

class FirstScreen extends StatefulWidget {
  const FirstScreen({Key? key}) : super(key: key);

  @override
  State<FirstScreen> createState() => _FirstScreenState();
}

class _FirstScreenState extends State<FirstScreen> {
  @override
  Widget build(BuildContext context) {
    return Login(showCreateAccountBtn: _onCreateAccountTapped());
  }

  Function(void)? _onCreateAccountTapped() {
    print("Click on Create Acc");

    return null;
  }
}

Here is the GIST link (not working for unknown reasons): https://dartpad.dev/?id=58294fa8eed37b016d0b257fee2f1317

Thanks for reading this !