create a link without a place just with description

This is zim 0.54
Python version is (2, 6, 5, 'final', 0)
Gtk version is (2, 20, 1)
Pygtk version is (2, 17, 0)
Platform is posix
No bzr version-info found

======= Traceback =======
  File "/usr/lib/pymodules/python2.6/zim/gui/widgets.py", line 2258, in do_response
    destroy = self.do_response_ok()
  File "/usr/lib/pymodules/python2.6/zim/gui/pageview.py", line 5398, in do_response_ok
    attrib['src'] = self.ui.notebook.relative_filepath(file, self.path) or file.uri
  File "/usr/lib/pymodules/python2.6/zim/notebook.py", line 1840, in relative_filepath
    if file.ischild(attachments_dir):
AttributeError: 'NoneType' object has no attribute 'ischild'