title: Django rest Framework - Expected a list of items but got type "QuerySet"
body: <p>I try to serialize query set. But Im getting <strong>{'non_field_errors': [ErrorDetail(string='Expected a list of items but got type "QuerySet".', code='not_a_list')]}</strong> error. How to solve this error. </p>
  
  <pre><code>    def post(self, request):
          data = request.data
          user_name = data.get('username')
          signup_filtered_data = Signup.objects.filter(username= user_name).values()
          print(signup_filtered_data)
          serializer = SignupSerializer(data= signup_filtered_data, many=True)
          serializer.is_valid()
          print(serializer.errors)
          signup_jason_data = json.dumps(serializer.data)
          return HttpResponse(signup_jason_data)
  </code></pre>
  
  <p>models.py</p>
  
  <pre><code>class Signup(models.Model):
      first_name = models.CharField(max_length=50, blank=True, null=True)
      last_name = models.CharField(max_length=50, blank=True, null=True)
      email = models.EmailField(max_length=50, unique= True)
      phone_number = models.CharField(max_length=12, unique= True)
      username = models.CharField(max_length=50, unique= True)
      password = models.CharField(max_length=50, blank=True, null=True)
  </code></pre>
  
  <p>serializers.py</p>
  
  <pre><code>class SignupSerializer(serializers.ModelSerializer):
  
      class Meta:
          model = Signup
          fields = '__all__'
  </code></pre>