问主体可能会导致返回'null‘，但是返回类型'FutureOr<List<Map<dynamic，dynamic>是一个潜在的不可空类型。

EN

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

import 'package:algorithm_learn/sqldb.dart';
import 'package:flutter/material.dart';

class Home extends StatefulWidget {
  const Home({super.key});

  @override
  State<Home> createState() => _HomeState();
}

class _HomeState extends State<Home> {
  SqlDb sqlDb = SqlDb();
  bool isloading = true;
  List coing = [];

  Future<List<Map>> readData() async {
    List<Map> response = await sqlDb.readData("SELECT * FROM 'Coing'");    //(ERROR IS HERE)
    coing.addAll(response);
    isloading = false;
    if (this.mounted) {
      setState(() {});
    }
  }

  @override
  void initState() {
    readData();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('HomePage'),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          Navigator.of(context).pushNamed("addperson");
        },
        child: const Icon(Icons.add),
      ),
      body: isloading == true ?
      Center(child: Text("Loading..."))
       : Container(
        child: ListView(
          children: [
            MaterialButton(
              onPressed: () async {
                await sqlDb.mydeleteDatabase();
              },
              child: const Text("Delete Database"),
            ),
            ListView.builder(
              itemCount: coing.length,
              physics: NeverScrollableScrollPhysics(),
              shrinkWrap: true,
              itemBuilder: (context, i) {
                return Card(
                  child: ListTile(
                    title: Text("${coing[i]['first_name']}"),
                    subtitle: Text("${coing[i]['last_name']}"),
                    trailing: IconButton(
                      onPressed: () async {
                        int response = await sqlDb.deleteData(
                            "DELETE FROM coing WHERE id = ${coing[i]['id']}");
                        if (response > 0) {
                          coing.removeWhere(
                              (element) => element["id"] == coing[i]['id']);
                          setState(() {});
                        }
                      },
                      icon: Icon(Icons.delete, color: Colors.red),
                    ),
                  ),
                );
              },
            ),
          ],
        ),
      ),
    );
  }
}