【Flutter】「The method ‘[]’ can’t be unconditionally invoked because the receiver can be ‘null’.」の意味と対策

Flutterのエラー「The method ‘[]’ can’t be unconditionally invoked because the receiver can be ‘null’.」の意味と対策について紹介します。

「The method ‘[]’ can’t be unconditionally invoked because the receiver can be ‘null’.」の意味

Flutterでデバッグすると以下のようなエラーが出ることがあります。

The method '[]' can't be unconditionally invoked because the receiver can be 'null'. (Documentation)  Try making the call conditional (using '?.') or adding a null check to the target ('!').

              key: Key(todos[position].id.toString()),
              onDismissed: (direction) {
                int id = todos[position].id;
                String title = todos[position].title.toString();
                setState(() {
                  todos?.removeAt(position);
                  helper.deleteTodo(id);
                  getData();
                });