Test fixed modlist generation code

https://fedorahosted.org/freeipa/ticket/4138
Reviewed-By: Jan Cholasta <jcholast@redhat.com>

ipatests/test_xmlrpc/test_attr.py

@@ -278,6 +278,12 @@ class test_attr(Declarative):
             ),
         ),
 
+        dict(
+            desc='Try to "remove" empty location from %r' % user1,
+            command=('user_mod', [user1], dict(l=None)),
+            expected=errors.EmptyModlist(),
+        ),
+
         dict(
             desc='Lock %r using setattr' % user1,
             command=(