old_contents: from django.contrib import admin
  from django.contrib.auth import get_user_model
  
  # Register your models here.
  admin.site.register(get_user_model())
  
new_contents: from django.contrib import admin
  from django.contrib.auth import get_user_model
  from django.contrib.auth.admin import UserAdmin
  
  # Register your models here.
  admin.site.register(get_user_model(), UserAdmin)
  
subject: use the UserAdmin admin