I'm trying to create a package of content objects but I've the following error:

Fatal error: Call to a member function getElementsByTagName() on a non-object in /var/www/ezpublish-4.1.1/kernel/classes/datatypes/ezobjectrelationlist/ezobjectrelationlisttype.php on line 1646
Fatal error: eZ Publish did not finish its request

Steps to reproduce

1. Setup -> Package -> Create new package
2. Content object export
3. Add subtree
4. NO Include class definitions
NO Include templates related to exported objects
YES Published version
Only one language
YES Keep all in selected nodes
YES Keep all in selected nodes
5. Package information
6. Package maintainer
7. Package changelog
8. Fatal error