plugin XEP-0050: fixed crash on empty node in addAdHocCommand

src/plugins/plugin_xep_0050.py

@@ -483,8 +483,7 @@ class XEP_0050(object):
         """
         # FIXME: "@ALL@" for profile_key seems useless and dangerous
 
-        node = node.strip()
-        if not node:
+        if node is None:
             node = "%s_%s" % ('COMMANDS', uuid4())
 
         if features is None: