How can I remove empty fields when recursing?

Question

Django

Good afternoon. Rucursively sterilizing hierarchical data.
Is it possible in serializers not to display a field at all, but not to display an empty one?

class HierarchicalTag(MPTTModel, TagBase):
    name = models.CharField(max_length=50, unique=True)
    parent = TreeForeignKey('self', null=True, blank=True, related_name='children', db_index=True, on_delete=models.CASCADE)

    def __str__(self):
        return self.name

    class MPTTMeta:
        order_insertion_by = ['name']

    def __unicode__(self):
        return self.name

view

class TagsList(generics.ListAPIView):
    serializer_class = ReadHierarchicalTagSerializer
    permission_classes = [permissions.IsAuthenticatedOrReadOnly]

    def get_queryset(self):
        return HierarchicalTag.objects.root_node(tree_id=1).get_ancestors(include_self=True)

serializers

class ReadHierarchicalTagSerializer(serializers.ModelSerializer):
    user = serializers.SerializerMethodField()
    children = serializers.ListField(child=RecursiveField(), source='get_children', read_only=True)

    class Meta:
        model = HierarchicalTag
        fields = ['id', 'name', 'children', 'user']

    def get_user(self, model):
        if TaggedContentItem.objects.filter(tag_id=model.id).exists():
            return [o.content_object.user.username for o in TaggedContentItem.objects.filter(tag_id=model.id)]

json_data

{
                        "id": 36,
                        "name": "MS Project",
                        "children": [],
                        "user": null
                    }