Fixed a problems with the get_history method

greenmine/projects/issues/serializers.py

@@ -70,6 +70,7 @@ class IssueSerializer(serializers.ModelSerializer):
         diff_list = []
         current = None
 
+        if obj:
             for version in reversed(list(reversion.get_for_object(obj))):
                 if current:
                     issues_diff = self.get_issues_diff(current, version)

greenmine/projects/tasks/serializers.py

@@ -53,6 +53,7 @@ class TaskSerializer(serializers.ModelSerializer):
         diff_list = []
         current = None
 
+        if obj:
             for version in reversed(list(reversion.get_for_object(obj))):
                 if current:
                     task_diff = self.get_task_diff(current, version)

greenmine/projects/userstories/serializers.py

@@ -84,6 +84,7 @@ class UserStorySerializer(serializers.ModelSerializer):
         diff_list = []
         current = None
 
+        if obj:
             for version in reversed(list(reversion.get_for_object(obj))):
                 if current:
                     us_diff = self.get_user_stories_diff(current, version)