diff --git a/python_apps/media-monitor2/media/monitor/pure.py b/python_apps/media-monitor2/media/monitor/pure.py
index a879f449f..958e1d950 100644
--- a/python_apps/media-monitor2/media/monitor/pure.py
+++ b/python_apps/media-monitor2/media/monitor/pure.py
@@ -154,6 +154,9 @@ def walk_supported(directory, clean_empties=False):
     that support the extensions we are considering. When clean_empties
     is True we recursively delete empty directories left over in
     directory after the walk. """
+    if directory is None:
+        return
+
     for root, dirs, files in os.walk(directory):
         full_paths = ( os.path.join(root, name) for name in files
                 if is_file_supported(name) )
@@ -162,8 +165,7 @@ def walk_supported(directory, clean_empties=False):
 
 
 def file_locked(path):
-    cmd = "lsof %s" % path
-    f = Popen(cmd, shell=True, stdout=PIPE).stdout
+    f = Popen(["lsof", path], stdout=PIPE).stdout
     return bool(f.readlines())
 
 def magic_move(old, new, after_dir_make=lambda : None):