Submitting a blank "From Date" in Datestamp field is defaulting to a 0 timestamp, 1970, when saved into the database

The empty field value was being updated in the Datestamp fields when these were submitted to the database.

Core settings:
Type - datestamp field (date field is working)
Widget - jscalendar (that is passing back an empty string '')
Timezone - Brisbane/Australia
Multiple option - No
Required option - No

I tracked the problem into the hook_field 'date_field', where the function 'date_unset_granularity' was converting the zero length string into an invalid date. I resolved the issue myself by setting the value to equal to NULL in the event of an empty string, otherwise, use the 'date_unset_granularity' function, as shown by the SVN patch below:

    Index: C:/Users/Alan/workspace/CaignWebs/sites/all/modules/date/date.module
===================================================================
--- C:/Users/Alan/workspace/CaignWebs/sites/all/modules/date/date.module  (revision 146)
+++ C:/Users/Alan/workspace/CaignWebs/sites/all/modules/date/date.module  (working copy)
@@ -116,8 +116,8 @@
       // so that won't work in the field, and doing it in the widget get much more complex, so leaving it here for now.
       foreach ($items as $delta => $item) {
         foreach ($process as $processed) {
-          if (!form_get_errors()) {
-            $replace = date_unset_granularity($item[$processed], date_granularity_array($field), $field['type']);
+          if (!form_get_errors()) {
+            $replace = ($item[$processed] != '') ? date_unset_granularity($item[$processed], date_granularity_array($field), $field['type']) : NULL;
             $items[$delta][$processed] = $replace !== 'ERROR' && $replace != $items[$delta][$processed] ? $replace : $items[$delta][$processed];
           }
         }

Regards

Alan