make ldap_wallet_name parameter Optional

manifests/init.pp

@@ -13,7 +13,7 @@ class secure_afs_request (
   Enum['wallet', 'none']    $db_credentials_source = 'wallet',
   Optional[String]          $db_wallet_name        = undef,
   #
-  String                    $ldap_wallet_name = undef,
+  Optional[String]          $ldap_wallet_name      = undef,
 ) {
 
   # Install the software.