[Flutter] Getting the exception "This will throw an exception in the future. For now it is...

I'm new to Flutter and facing some difficulties. I'm building an expense tracking app and trying to implement a database using the sqflite package. However, whenever I attempt to add a new transaction, I get the exception 'This will throw an exception in the future. For now it is displayed once per type' in the debug console, and the app freezes. Am I misusing a callback function? The Relevant code follows:

Here is my DB definition and operations code:

class DbUtil {
DbUtil._();
static final DbUtil instance = DbUtil._();
static Database? _database;

get database async {
if (_database != null) return _database;

_database = await _initDatabase();
return _database;
}

_initDatabase() async {
return await sql.openDatabase(
path.join(await sql.getDatabasesPath(), 'transactions.db'),
version: 1,
onCreate: _onCreate,
);
}

_onCreate(Database db, int version) async {
await db.execute(
'CREATE TABLE transactions (id TEXT PRIMARY KEY, title TEXT, value FLOAT, date DATE ,category TEXT)');
}

Future<void> insert(String table, Map<String, Object> data) async {
final db = await database;
await db.insert(table, data,
conflictAlgorithm: sql.ConflictAlgorithm.replace);
}
}


Next, my main.dart (I removed some code to keep it concise on what is relevant):

void main() {
runApp(const MyApp());
}

class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);

@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'My Expenses',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(),
);
}
}

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

@override
State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
List<Category>? category;

final _baseUrl = 'https://expenses-a210d-default-rtdb.firebaseio.com/';

List<Transact> _transactions = [];

_openTransactionFormModal(BuildContext context) {
showModalBottomSheet(
context: context,
builder: (_) {
return TransactionForm(_addTransaction);
},
);
}

_addTransaction(String title, double value, DateTime date, String category) {
final newTransaction = Transact(
id: Random().nextDouble().toString(),
title: title,
value: value,
date: date,
category: category,
);
setState(() {
_transactions.add(newTransaction);
_sumTotalCategory(newTransaction);
_addToDb(newTransaction);
});

Navigator.of(context).pop();
}

_addToDb(transaction) async {
await DbUtil.instance.insert(
'transactions',
{
'id': transaction.id,
'title': transaction.title,
'value': transaction.value,
'date': transaction.date,
'category': transaction.category,
},
);
}

@override
Widget build(BuildContext context) {
final appBar = AppBar(
title: Text(
'Despesas Pessoais',
style: TextStyle(
fontSize: 20 * MediaQuery.of(context).textScaleFactor,
),
),
actions: [
// IconButton(
// onPressed: () => loadTransactions(),
// icon: Icon(Icons.refresh),
// ),
IconButton(
onPressed: () => _openTransactionFormModal(context),
icon: Icon(Icons.add),
),
]);
final availableHeight = MediaQuery.of(context).size.height -
appBar.preferredSize.height -
MediaQuery.of(context).padding.top;
return Scaffold(
appBar: appBar,
body: SingleChildScrollView(
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
PieChartExpenses(valueSum),
Container(
width: double.infinity,
child: Card(
color: Color.fromARGB(255, 2, 84, 90),
elevation: 5,
child: total_sum(valueSum: valueSum),
),
),
Container(
height: availableHeight * 0.7,
child: Column(
children: [
TransactionList(_transactions, _removeTransaction),
],
),
),
],
),
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () => _openTransactionFormModal(context),
),
floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
);
}
}



I attempted to modify the insert function based on the solution from this answer, but it didn't work. I also tried modifying the function to close the database afterward, but that had no effect either. From what I can tell, the database isn't even being opened.

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