Index: includes/webform.components.inc
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/webform/includes/webform.components.inc,v
retrieving revision 1.25.2.26
diff -u -r1.25.2.26 webform.components.inc
--- includes/webform.components.inc	20 Oct 2010 02:35:42 -0000	1.25.2.26
+++ includes/webform.components.inc	20 Oct 2010 02:58:22 -0000
@@ -933,10 +933,12 @@
  * Validate an element value is unique with no duplicates in the database.
  */
 function webform_validate_unique($element, $form_state) {
-  $nid = $form_state['values']['details']['nid'];
-  $sid = $form_state['values']['details']['sid'];
-  $count = db_result(db_query("SELECT count(*) FROM {webform_submitted_data} WHERE nid = %d AND cid = %d AND sid <> %d AND LOWER(data) = '%s'", $nid, $element['#webform_component']['cid'], $sid, $element['#value']));
-  if ($count) {
-    form_error($element, t('The value %value has already been submitted once for the %title field. You may have already submitted this form, or you need to use a different value.', array('%value' => $element['#value'], '%title' => $element['#title'])));
+  if ($element['#value'] !== '') {
+    $nid = $form_state['values']['details']['nid'];
+    $sid = $form_state['values']['details']['sid'];
+    $count = db_result(db_query("SELECT count(*) FROM {webform_submitted_data} WHERE nid = %d AND cid = %d AND sid <> %d AND LOWER(data) = '%s'", $nid, $element['#webform_component']['cid'], $sid, $element['#value']));
+    if ($count) {
+      form_error($element, t('The value %value has already been submitted once for the %title field. You may have already submitted this form, or you need to use a different value.', array('%value' => $element['#value'], '%title' => $element['#title'])));
+    }
   }
 }