Traceback (most recent call last):
  File "/usr/sbin/update-apt-xapian-index", line 104, in <module>
    indexer.rebuild(opts.pkgfile)
  File "/usr/lib/python2.7/dist-packages/axi/indexer.py", line 715, in rebuild
    self.buildIndex(dbdir, generator)
  File "/usr/lib/python2.7/dist-packages/axi/indexer.py", line 690, in buildIndex
    for doc in documents:
  File "/usr/lib/python2.7/dist-packages/axi/indexer.py", line 562, in gen_documents_apt
    yield self.get_document_from_apt(pkg)
  File "/usr/lib/python2.7/dist-packages/axi/indexer.py", line 530, 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 &'