Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.265
diff -u -p -r1.265 form.inc
--- includes/form.inc	4 Feb 2008 10:23:32 -0000	1.265
+++ includes/form.inc	5 Feb 2008 02:01:49 -0000
@@ -664,10 +664,10 @@ function _form_validate($elements, &$for
   // Validate the current input.
   if (!isset($elements['#validated']) || !$elements['#validated']) {
     if (isset($elements['#needs_validation'])) {
-      // We only check for trimmed string length being zero. 0 might be
-      // a possible value with some field types, such as radio buttons, so
-      // empty() is not usable here.
-      if ($elements['#required'] && strlen(trim($elements['#value'])) == 0) {
+      // Use count() to check that arrays are not empty, and then check the
+      // trimmed string length since '0' is a valid possible value with some
+      // field types, so empty() is not usable here.
+      if ($elements['#required'] && (!count($elements['#value']) || (is_string($elements['#value']) && strlen(trim($elements['#value'])) == 0))) {
         form_error($elements, $t('!name field is required.', array('!name' => $elements['#title'])));
       }