Check for empty/single value parameters before calling callbacks

https://fedorahosted.org/freeipa/ticket/2701

tests/test_xmlrpc/test_config_plugin.py

@@ -21,6 +21,7 @@
 Test the `ipalib/plugins/config.py` module.
 """
 
+from ipalib import errors
 from xmlrpc_test import Declarative, fuzzy_digits, fuzzy_uuid
 
 class test_config(Declarative):
@@ -52,4 +53,11 @@ class test_config(Declarative):
                 ),
         ),
 
+        dict(
+            desc='Try to remove ipausersearchfields',
+            command=('config_mod', [],
+                dict(delattr=u'ipausersearchfields=uid,givenname,sn,telephonenumber,ou,title')),
+            expected=errors.RequirementError(name='ipausersearchfields'),
+        ),
+
     ]