Import from recent files makes troubles

Openshot version 1.4.2, installed on Debian wheezy from testing repository.

The first import from recent files goes fine. But after it the import button doesn't work anymore.
Launching from terminal, it gives the following error:

on_tlbImportFiles_clicked called with self.GtkToolButton
Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.7/openshot/windows/MainGTK.py", line 1781, in on_tlbImportFiles_clicked
    self.import_files_dialog = AddFiles.frmAddFiles(form=self, project=self.project)
  File "/usr/lib/pymodules/python2.7/openshot/windows/AddFiles.py", line 47, in __init__
    self.frmAddFiles.set_current_folder(preferences.Settings.app_state["import_folder"])
TypeError: Gtk.FileChooser.set_current_folder() argument 1 must be string, not None

Bug seems to be solved changing line 46 of openshot/windows/AddFiles.py , from:
 if default_folder != "None":
to:
if default_folder != None: