title: AttributeError when trying to created nested serializer in Django REST Framework
body: <p>I have two models of sets, and cards. Theses models have one to many relationship where there are many cards in a single set. These model are join by a foreign key -  each card has <code>set_id</code> which is equal to the <code>id</code> of the set. These IDs are <code>UUID</code>.</p>
  <p>I am trying to create a serializer using Django REST Framework where I return the details of the set, as well as including all the cards that are part of the set.</p>
  <p><strong>error</strong></p>
  <pre><code>Got AttributeError when attempting to get a value for field `cards` on serializer `SetSerializers`.
  The serializer field might be named incorrectly and not match any attribute or key on the `Set` instance.
  Original exception text was: 'Set' object has no attribute 'cards'.
  </code></pre>
  <p><strong>serializers.py</strong></p>
  <pre class="lang-py prettyprint-override"><code>class CardSerializers(serializers.ModelSerializer):
      class Meta:
          model = Card
          fields = ['id', 'number', 'name', 'set_id']
  
  class SetSerializers(serializers.ModelSerializer):
      cards = CardSerializers()
  
      class Meta:
          model = Set
          fields = ['id', 'code', 'name', 'releaseDate','cards']
  
  </code></pre>
  <p><strong>models.py</strong></p>
  <pre class="lang-py prettyprint-override"><code>class Set(models.Model):
      id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
      ...
  
      objects = models.Manager()
  
      def __str__(self):
          return self.name
  
  class Card(models.Model):
      id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
      ...
      set = models.ForeignKey(Set, on_delete=models.CASCADE, related_name='Cards', related_query_name='Cards')
  
  
      objects = models.Manager()
  
      def __str__(self):
          return self.name
  </code></pre>
  <p><strong>views.py</strong></p>
  <pre class="lang-py prettyprint-override"><code>class SetsIndividualData(ListAPIView):
      serializer_class = SetSerializers
  
      def get_queryset(self):
          setCode = self.kwargs.get('setCode')
          queryList = Set.objects.filter(code=setCode.upper())
          return queryList
  </code></pre>