fix error

aircox/models/program.py

@@ -132,7 +132,7 @@ class Program(Page):
 
         # TODO: move in signals
         path_ = getattr(self, '__initial_path', None)
-        abspath = os.path.join(conf.MEDIA_ROOT, path_)
+        abspath = path_ and os.path.join(conf.MEDIA_ROOT, path_)
         if path_ is not None and path_ != self.path and \
                 os.path.exists(abspath) and not os.path.exists(self.abspath):
             logger.info('program #%s\'s dir changed to %s - update it.',