اررور آپدیت

سلام وقتتون بخیر من دارم آپدیتمو با ایجکس مینویسم ولی نمیدونم چرا همچین ارروری دارم

Call to a member function update() on null

کد توی کنترلرم:

 
 
        $idAnswer=$answeredQuestionRequest->answerId;
        $answerId=Answer::find($idAnswer);
 
        $idQuestion=$answeredQuestionRequest->questionId;
        $questionId=Question::find($idQuestion);
 
        $correctAnswer=$answerId->correct_answer;
        $answer=$answeredQuestionRequest->answer;
        $answerQuestion=([
            "answer_id"=>$answerId->id,
            "answer_select_user"=>$answer,
            "is_true"=>empty($answer) ? '۲' : ($correctAnswer==$answer ? '۱' : '۰')
        ]);
        $update=AnsweredQuestions::find($questionId->id)->update($answerQuestion);
 
        return $update;
    }```
 
کد ایجکسم:
``` $('.prev').on('click',function () {
        if (number > question_id) {
            console.log(number--);
            $('.s-holder').hide();
            $('#s' + number).show();
        }
 
        $('#next').on('click',function () {
            var id = $(this).data('id');
            var answerId = $('#answerId' + id).val();
            var lai = $(this).data('answer_id');
            // console.log(lai);
            var answer = $('input[name=' + lai + ']:checked').val();
            var questionId = $('#questionId' + id).val();
            // console.log(answer);
            $.ajax({
                type:"POST",
                url:"{{route('front.exam.update',$link)}}",
                data: {
                    'id':id,
                    'questionId': questionId,
                    'answerId': answerId,
                    'answer' : answer,
                    '_token': '{{csrf_token()}}'
                },
                success:function (data) {
                    alert(answerId);
                    if (data==۱){
                        alert('movafagh');
                    }
                }
            });
        });
    });```
 
اینم روتم:
```Route::post('/exam/edit/{link}/','Front\ExamController@update')->name('front.exam.update');```