Create a default producr if one was not set.

dc_add_default_product.module

/**
 * Implements hook_form_alter().
 */
function dwwcommerce_form_alter(&$form, &$form_state, $form_id) {
  // The style edit form.
  if ($form_id == 'product_style_node_form') {
    // Add a custom submit.
    $form['actions']['submit']['#submit'][] = 'mymodule_node_prod_display_form_submit';
  }
}

/**
 * A custom submit for the product style form.
 *
 * Used to set the default product if not allready set.
 */
function mymodule_node_prod_display_form_submit($form, &$form_state) {
  $nid = $form_state['values']['nid'];
  $node = node_load($nid);

  if ($node->type = 'product_style') {
    if (empty($node->field_product)) {
      // Add Awaiting Product.
      $node->field_product[LANGUAGE_NONE][]['product_id'] = AWAITING_PRODUCT_ID;
    }
    node_save($node);
  }
}