The Flutter Error show that " A non-null value must be returned since the return type 'Widget' doesn't allow null "

Is that anything wrong? BUt I had write a return statement

The Error

Widget _buildCommentList() {
    return ListView.builder(itemBuilder: (context, index) {
       if (index < _comments.length) {
      return _buildCommentItem(_comments[index]);
       }
    });
  }

The body might complete normally, causing 'null' to be returned, but the return type, 'Widget', is a potentially non-nullable type.Try adding either a return or a throw statement at the end.

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:penang_beachess/blog_page/blog_page.dart';
import 'package:flutter/material.dart';
import 'package:penang_beachess/models/user_model.dart';
import 'Post.dart';


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

  @override
  State<CommentPlugin> createState() => _CommentPluginState();
}

class _CommentPluginState extends State<CommentPlugin> {
  List<String> _comments = [];

  void _addComment(String val) {
    setState(() {
      _comments.add(val);
    });
  }

  Widget _buildCommentList() {
    return ListView.builder(itemBuilder: (context, index) {
       if (index < _comments.length) {
      return _buildCommentItem(_comments[index]);
       }
    });
  }

  Widget _buildCommentItem(String comment) {
    return Card(
      child: ListTile(
        title: Text("${loggedInUser.username}"),
        title: Text(comment),
      ),
    );
  }

  User? user = FirebaseAuth.instance.currentUser;
  UserModel loggedInUser = UserModel();

  @override
  void initState() {
    super.initState();
    FirebaseFirestore.instance
        .collection("users")
        .doc(user!.uid)
        .get()
        .then((value) {
      this.loggedInUser = UserModel.fromMap(value.data());
      setState(() {});
    });
  }

  @override
  Widget build(BuildContext context) {
    return Center(
        child: IconButton(
      icon: const Icon(
        Icons.chat_bubble_outline,
        color: Colors.grey,
        size: 36,
      ),
      onPressed: () {
        showModalBottomSheet(
            shape: const RoundedRectangleBorder(
              borderRadius: BorderRadius.vertical(top: Radius.circular(25.0)),
            ),
            backgroundColor: Colors.white,
            context: context,
            isScrollControlled: true,
            builder: (context) {
              return Column(
                mainAxisSize: MainAxisSize.min,
       
                children: <Widget>[
                  Row(
                    children: [
                      IconButton(
                        icon: Icon(Icons.arrow_back, color: Colors.blue),
                        onPressed: () {
                          Navigator.of(context).pop();
                        },
                      ),
                      const Text('Back'),
                    ],
                  ),
                  Expanded(child: _buildCommentList()),
                  TextField(
                    onSubmitted: (String submitedStr) {
                      _addComment(submitedStr);
                    },
                    cursorColor: Colors.black,
                    maxLength: 20,
                    decoration: const InputDecoration(
                      filled: true,
                      icon: Icon(Icons.chat_bubble_outline),
                      contentPadding: EdgeInsets.fromLTRB(20, 15, 20, 15),
                      hintText: "Write a comment...",
                     
                    ),
                  ),
                  // )),
                ],
              );
            });
      },
    ));
  }
}