Handle missing url attribute on write requests

orchestra/api/serializers.py

@@ -64,7 +64,10 @@ class HyperlinkedModelSerializer(serializers.HyperlinkedModelSerializer):
 class RelatedHyperlinkedModelSerializer(HyperlinkedModelSerializer):
     """ returns object on to_internal_value based on URL """
     def to_internal_value(self, data):
-        url = data.get('url')
+        try:
+            url = data.get('url')
+        except AttributeError:
+            url = None
         if not url:
             raise ValidationError({
                 'url': "URL is required."