Traceback (most recent call last):
  File "/usr/sbin/update-apt-xapian-index", line 102, in <module>
    indexer.incrementalUpdate()
  File "/usr/lib/python2.7/dist-packages/axi/indexer.py", line 669, in incrementalUpdate
    self.updateIndex(dbpath)
  File "/usr/lib/python2.7/dist-packages/axi/indexer.py", line 651, in updateIndex
    db.add_document(self.get_document_from_apt(pkg))
  File "/usr/lib/python2.7/dist-packages/axi/indexer.py", line 531, in get_document_from_apt
    addon.obj.index(document, pkg)
  File "/usr/share/apt-xapian-index/plugins/software-center.py", line 114, in index
    document.add_value(XapianValues.ICON_URL, url)
ValueError: invalid null reference in method 'Document_add_value', argument 3 of type 'std::string const &'