Sample to option in drupal node_type_form

my.module

function hook_form_node_type_form_alter(&$form, $form_state) {
  $form['workflow']['node_options']['#options']['sample'] = t('Sample');
  $form['workflow']['node_options']['rotativa']['#description'] = t('Sample enable');
  //$form['#validate'][] = 'rotativa_node_type_form_validate';
}

/* Validate if Sample is active*/

function my_node_type_valid($type) {
  $options = variable_get("node_options_$type", array());
  if (in_array('sample', $options)) {
    return TRUE;
  }
  return FALSE;
}