fix isinstance() check on get_queryset()
fix isinstance() check on get_queryset()

j1z0/django-rest-framework-mongoengine,shinSG/django-rest-framework-mongoengine,iorlas/django-rest-framework-mongoengine,nicolascine/django-rest-framework-mongoengine,9nix00/django-rest-framework-mongoengine,arpitgoyaiitkgp/django-rest-framework-mongoengine,lewang0418/django-rest-framework-mongoengine,BurkovBA/django-rest-framework-mongoengine,umutbozkurt/django-rest-framework-mongoengine,tweiand-10m2/django-rest-framework-mongoengine,arpitgoyalhtmedia/django-rest-framework-mongoengine,BryanAke/django-rest-framework-mongoengine,foundi/django-rest-framework-mongoengine,optik/django-rest-framework-mongoengine,9nix00/django-rest-framework-mongoengine-hack,pombredanne/django-rest-framework-mongoengine