How to force-save an “empty”/unchanged django admin inline?

It took me quite some time to figure out but it is actually really simple.

from django.contrib import admin
from django.forms.models import BaseInlineFormSet, ModelForm

class AlwaysChangedModelForm(ModelForm):
    def has_changed(self):
        """ Should returns True if data differs from initial. 
        By always returning true even unchanged inlines will get validated and saved."""
        return True

class CheckerInline(admin.StackedInline):
    """ Base class for checker inlines """
    extra = 0
    form = AlwaysChangedModelForm