Index: form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.265.2.1
diff -u -r1.265.2.1 form.inc
--- form.inc	4 Feb 2008 16:24:29 -0000	1.265.2.1
+++ form.inc	5 Feb 2008 16:03:39 -0000
@@ -664,11 +664,14 @@
   // Validate the current input.
   if (!isset($elements['#validated']) || !$elements['#validated']) {
     if (isset($elements['#needs_validation'])) {
-      // An empty textfield returns '' so we use empty(). An empty checkbox
-      // and a textfield could return '0' and empty('0') returns TRUE so we
-      // need a special check for the '0' string.
-      if ($elements['#required'] && empty($elements['#value']) && $elements['#value'] !== '0') {
-        form_error($elements, $t('!name field is required.', array('!name' => $elements['#title'])));
+      // Make sure a value is passed when the field is required.
+      if ($elements['#required']) {
+        // A simple call to empty() will not cut it here as some fields, like
+        // checkboxes, can return a valid value of '0'. Instead, check the
+        // length if it's a string, and the item count if it's an array.
+        if (!count($elements['#value']) || (is_string($elements['#value']) && strlen(trim($elements['#value'])) == 0)) {
+          form_error($elements, $t('!name field is required.', array('!name' => $elements['#title'])));
+        }
       }
 
       // Verify that the value is not longer than #maxlength.