Added a model for event state (including data migration, signal based

notifications, etc.)

dav_events/forms/generic.py

@@ -2,6 +2,7 @@ import logging
 from django import forms
 from django.apps import apps
 from django.core.exceptions import ImproperlyConfigured
+from django.db.models.manager import Manager
 
 from .. import converters
 
@@ -165,8 +166,11 @@ class ModelMixin(object):
         data = {}
         for field in instance._meta.get_fields():
             v = getattr(instance, field.name)
-            if v is not None:
-                data[field.name] = getattr(instance, field.name)
+            if v is None:
+                continue
+            if isinstance(v, Manager):
+                continue
+            data[field.name] = getattr(instance, field.name)
         self.is_bound = True
         self.data = data
         return data