Paginaton in nested view in ViewSet in custom route [Django - Rest Framework]

utils.py

from django.core.paginator import Paginator, EmptyPage, PageNotAnInteger, InvalidPage
from django.http import Http404
from django.utils import six
from rest_framework import pagination


def get_paginated_serializer(queryset, request, serializer_class, context,
                              page_size=50, page_kwarg='page', *args, **kwargs):
    '''Get paginated serializer loaded with all the data'''
    paginator = Paginator(queryset, page_size)
    page_kw = kwargs.get(page_kwarg)
    page_query_param = request.query_params.get(page_kwarg)
    page = page_kw or page_query_param or 1

    try:
        page_number = paginator.validate_number(page)
    except InvalidPage:
        if page == 'last':
            page_number = paginator.num_pages
        else:
            raise  Http404("Page is not 'last', nor can it be converted to an int.")

    try:
        queryset = paginator.page(page_number)
    except InvalidPage as exc:
        error_format = _('Invalid page (%(page_number)s): %(message)s')
        raise Http404(error_format % {
            'page_number': page_number,
            'message': six.text_type(exc)
        })

    class PaginatedSerializer(pagination.PaginationSerializer):
                class Meta:
                    object_serializer_class = serializer_class
    serializer = PaginatedSerializer(instance=queryset, context=context)
    return serializer

views.py

class UserViewSet(viewsets.ModelViewSet):
    lookup_field = 'username'
    serializer_class = UserSerializer
    queryset = User.objects.all()
    permission_classes = [IsAdminUserOrReadOnly]

    @list_route(methods=['GET'], url_path='(?P<username>[^/]+)/items',
                permission_classes=(permissions.AllowAny,))
    def items(self, request, username=None, *args, **kwargs):
        queryset = Items.objects.filter(user__username=username).select_related('images.count','images.first.thumb')
        
        # Get the paginated serializer
        serializer = utils.get_paginated_serializer(queryset, request, ItemSerializer, self.get_serializer_context(), 50)
        if not serializer.data['results'] and not User.objects.filter(username=username).exists():
            return Response(serializer.data, status=404)
        return Response(serializer.data)