Form validation handler for node_admin_nodes().
Checks whether any nodes have been selected to perform the chosen 'Update option' on.
node_multiple_delete_confirm()
node_multiple_delete_confirm_submit()
function node_admin_nodes_validate($form, &$form_state) {
// Error if there are no items to select.
if (!is_array($form_state['values']['nodes']) || !count(array_filter($form_state['values']['nodes']))) {
form_set_error('', t('No items selected.'));
}
}