Cast exception when validating @font-face rule with CSS level 2 profile

[correctmost]

Steps to reproduce:

1. Go to https://jigsaw.w3.org/css-validator/#validate_by_input+with_options
2. Select CSS level 2 as the profile
3. Paste @font-face {font-weight: 700;} into the textarea
4. Press the Check button

Error encountered:
class org.w3c.css.properties.css2.Css2Style cannot be cast to class org.w3c.css.properties.css2.font.Css2Style (org.w3c.css.properties.css2.Css2Style and org.w3c.css.properties.css2.font.Css2Style are in unnamed module of loader org.w3c.jigsaw.servlet.AutoReloadServletLoader @2bee1bfe)