fixed models definition

adim/models/annotables.py

@@ -41,7 +41,7 @@ class AOType(models.Model):
 
 
 class AOSchema(BaseSchema):
-    ao_types = models.ManyToManyField(AOType, blank=True, null=True)
+    ao_types = models.ManyToManyField(AOType, blank=True)
 
     class Meta:
         app_label = "adim"
@@ -99,7 +99,7 @@ class AnObj(BaseEntity):
     sharing_opts = JSONField(verbose_name=_("sharing options"), default="{}", blank=True)
     allow_public_publishing = models.BooleanField(verbose_name=_("allow public publishing"), default=False)
     members = models.ManyToManyField(User, verbose_name=_("members"), through='AnObjMembership',
-                                     related_name='shared_anobjs', blank=True, null=True)
+                                     related_name='shared_anobjs', blank=True)
 
     image = models.ImageField(upload_to=get_image_path, verbose_name=_("image"), blank=True, null=True)
     image_url = models.CharField(max_length=512, verbose_name=_("image url"), blank=True, null=True, default="")