aptdaemon does not support listing the files of a package

I am installing packages out of a Python program (system-config-printer) and want to list the files contained in the installed package via

----------
#!/usr/bin/python

from gi.repository import GLib, PackageKitGlib
import sys

package = sys.argv[1]

try:
    res = pk.resolve(PackageKitGlib.FilterEnum.NONE, [package],
                     None, lambda p, t, d: True, None)
except GLib.GError:
    sys.exit(1)
if res.get_exit_code() != PackageKitGlib.ExitEnum.SUCCESS:
    sys.exit(1)
package_ids = res.get_package_array()
if len(package_ids) <= 0:
    sys.exit(1)
package_id = package_ids[0].get_id()

try:
    res = pk.get_files([package_id], None, progress, None)
except GLib.GError:
    pass

files = res.get_files_array()
if not files:
    print []
print files[0].get_property('files')
----------

The result is always empty. I asked on IRC and this is due to missing implementation of listing files in aptdaemon.