Replaced deprecated NullBooleanField with BooleanField

dav_registration/models.py

@@ -221,8 +221,7 @@ class RegistrationStatus(models.Model):
     registration = models.OneToOneField(Registration, on_delete=models.CASCADE, related_name='status')
     updated_at = models.DateTimeField(auto_now=True)
     answered = models.BooleanField(_('Durch Tourleitung beantwortet'), default=False)
-    # TODO: NullBooleanField is marked deprecated
-    accepted = models.NullBooleanField(_('Zusage erteilt'))
+    accepted = models.BooleanField(_('Zusage erteilt'), null=True, blank=True)
 
     class Meta:
         verbose_name = _('Anmeldungsstatus')