title: Object of type 'ListSerializer' is not JSON serializable
body: <p>I want to get all customer data and responses and also remarks.
  This is model.py</p>
  
  <pre><code>class Customer(models.Model):
  
  name = models.CharField(max_length=200)
  email_address = models.CharField(max_length=200)
  phone_number = models.CharField(max_length=20)
  age = models.SmallIntegerField(default=14)
  remarks = models.ManyToManyField(Remark,null=True,blank=True)
  created_at = models.DateTimeField(auto_now_add=True)
  
  def __str__(self):
      return str(self.id)
  
  
  class Response(models.Model):
  
  question = models.ForeignKey(Question)
  customer = models.ForeignKey(Customer)
  response_text = models.CharField(max_length=100, null=True, blank=True)
  created_at = models.DateTimeField(auto_now_add=True)
  uuid = models.UUIDField()
  
  def __str__(self):
      return str(self.id)
  </code></pre>
  
  <p>This is serializers.py</p>
  
  <pre><code>class ResponseSerializer(ModelSerializer):
    class Meta:
      model = Response
      fields = '__all__'
  
  class RemarksSerializer(ModelSerializer):
    class Meta:
      model = Remark
      fields = '__all__'
  
  class CustomerInformationSerializer(ModelSerializer):
    remarks = RemarksSerializer(many=True)
    responses = serializers.SerializerMethodField()
  
    def get_responses(self, obj):
      responses = Response.objects.filter(customer=obj)
      return ResponseSerializer(responses, many=True)
  
    class Meta:
      model = Customer
      fields = ('name', 'email_address', 'phone_number', 'age', 'remarks', 'responses')
  </code></pre>
  
  <p>This is services.py</p>
  
  <pre><code>def customer_information(company_id=1):
    cus = Customer.objects.filter(remarks__company_id=company_id)
    return CustomerInformationSerializer(cus, many=True).data
  </code></pre>
  
  <p>This is views.py</p>
  
  <pre><code>class CustomerInformationView(APIView):
    def get(self, request):
       company_id = request.GET.get('company_id', 1)
       resp = {'data': customer_information(company_id)}
       return Response(data=resp, status=status.HTTP_200_OK)
  </code></pre>
  
  <p>This is url.py</p>
  
  <pre><code> url(r'^customer/$', CustomerInformationView.as_view()),
  </code></pre>
  
  <p>I'm having this problem. How can I solve this. Kindly guide me.</p>