title: Django Rest Framework Invalid serialization
body: <p>I am trying to serialize a dictionary into Relationship Serializer, the data gets serialized fine but the validator returns false    </p>
  
  <p><strong>RelationshipSerializer:</strong></p>
  
  <pre><code>class RelationshipSerializer(serializers.ModelSerializer):
  
      user = UserSerializer(read_only=False)
      related_user = UserSerializer(read_only=False)
  
      class Meta:
          model = models.Relationship
          fields = (
              'user',
              'related_user',
          )
  </code></pre>
  
  <p><strong>View:</strong></p>
  
  <pre><code>related_user_id = body["related_user"]
  related_user = models.User.objects.get(id=related_user_id)
  
  user = self.get_object()
  
  user_serializer = serializers.UserSerializer(user).data
  related_user_serializer = serializers.UserSerializer(related_user).data
  
  # user_serializer and related_user_serializer return valid data.
  
  data = {"user": user_serializer, "related_user": related_user_serializer}
  
  serializer = serializers.RelationshipSerializer(data=data)
  
  # Serializer works fine, it prints out data correctly    
  
  serializer.is_valid() # Returns false
  
  return Response(serializer.data)
  </code></pre>
  
  <p>When I log <code>serializer.errors</code> I get </p>
  
  <pre><code>{
      "required": "This field is required.",
      "null": "This field may not be null.",
      "invalid": "Invalid data. Expected a dictionary, but got {datatype}."
  }
  </code></pre>
  
  <p>I tried setting my serializer fields to <code>null = True</code> and <code>required = False</code> but still no luck</p>