old_contents: # from django.forms import widgets
  from rest_framework import serializers
  from .models import Timer
  
  
  class TimerSerializer(serializers.ModelSerializer):
      class Meta:
          model = Timer
  
new_contents: from rest_framework import serializers
  from .models import Timer
  
  
  class TimerSerializer(serializers.ModelSerializer):
      class Meta:
          model = Timer
  
subject: Update timer/serializers.py