[FIX] Fix issue in constraint function for res_users.

asterisk_click2dial/asterisk_click2dial.py

@@ -318,6 +318,7 @@ class res_users(osv.osv):
     def _check_validity(self, cr, uid, ids):
         for user in self.browse(cr, uid, ids):
             for check_string in [('Internal number', user.internal_number), ('Caller ID', user.callerid)]:
+                if check_string[1]:
                     try:
                         plom = check_string[1].encode('ascii')
                     except UnicodeEncodeError: