Don't work with django-material

[vladimirmyshkovski]

Hi!
I trying use django-categories with django-material (materialize css ui for django-admin), and when i go to admin/categories/category/, i get error:

AttributeError at /django-admin/categories/category/

'str' object has no attribute 'user'

This error arise when I use django-material, but if i use original django-admin, this error don't arise.
Where is it worth to look for a mistake?