Notice: Undefined property: stdClass::$price in uc_product_view() when previewing new product

Ubercart 7.x-3.1.

When I create a new product then preview it, I get the following error message:

    Notice: Undefined property: stdClass::$price in uc_product_view() (line 716 of /var/www/html/drupal/sites/all/modules/ubercart/uc_product/uc_product.module).
    Notice: Undefined property: stdClass::$price in uc_product_view() (line 716 of /var/www/html/drupal/sites/all/modules/ubercart/uc_product/uc_product.module).

The product can be saved normally, and nothing bad happens. There's just that error message.

Previewing an existing product (after editing it) does not cause this issue.

The product is a product class "book" with fields added for Author, publisher, number of pages, etc. It has no attributes.