fix traceback when empty call to list

cccli/commands/list.py

@@ -36,7 +36,7 @@ class Command_list(TqlCommand):
         # smart merge argument to have a tql
         tql = ""
         for arg in self.args:
-            if arg[0] in ("&", "|", "$", "^", "%"):
+            if len(arg) == 0 or arg[0] in ("&", "|", "$", "^", "%"):
                 tql += arg
             else:
                 tql += "&%s" % arg