Why can't I see the add fields TabularInline?

Want to do 0 extra, so that if necessary it was possible to add a row with fields, but links to "add" in the lower left corner are simply not there! tried every output, with attributes, without and so on, without changes. What could be wrong?

class ProviderPageInline(admin.TabularInline):
 model = ProviderPage
 fields = ['provider', 'type']
 can_delete = False
 show_change_link = True
 def get_extra(self, request, obj=None, **kwargs):
 extra = 1
 if obj:
 extra = 0
 return extra

class PageAdmin(admin.ModelAdmin):
 list_filter = ['city__name']
 inlines = [ProviderPageInline]
 prepopulated_fields = {'slug':("title",)}