Validate comment_admin_overview form submissions.
function comment_admin_overview_validate($form, &$form_state) {
$form_state['values']['comments'] = array_diff($form_state['values']['comments'], array(
0,
));
// We can't execute any 'Update options' if no comments were selected.
if (count($form_state['values']['comments']) == 0) {
form_set_error('', t('Select one or more comments to perform the update on.'));
}
}