"Leave blank" fallback doesn't work on edit (patch)

I want my users to create referencing nodes only from referenced nodes pages using links and once created this reference can't be edited. I thought "Leave blank" fallback behavior with "Use fallback behavior when editing content" checkbox set suits well for it but it fallbacks to autocomplete widget so naming it "leave blank" is nonsense. :-)
As i think there needs to be two separated fallback settings - for new and for edited nodes. Jast as a temporary solution a suggest the following patch dealing with "leave blank" issue.

ps: This module is awesome! :-)

--- nodereference_url.module.orig       2011-08-23 00:12:41.000000000 +0400
+++ nodereference_url.module    2011-08-23 11:37:21.000000000 +0400
@@ -394,7 +394,7 @@
   if (empty($referenced_nid) || (!empty($field['widget']['edit_fallback']) && !empty($items))) {
     // If not on a node/add page (such as editing a node that does not yet have
     // a reference), switch to using an autocomplete widget.
-    if (in_array($fallback, array('page_not_found', 'leave_blank')) && nodereference_url_get_nid($field_name) === FALSE) {
+    if (in_array($fallback, array('page_not_found')) && nodereference_url_get_nid($field_name) === FALSE) {
       $fallback = 'autocomplete';
     }

@@ -502,7 +502,7 @@
       }
       // Arguments must line up exactly if they're not a wildcard.
       elseif (arg($part) != $arg) {
-        $referenced_nid = FALSE;
+        $referenced_nid = NULL;
         break;
       }
     }