Cannot use theme omega after upgrading from Primefaces 8 to Primefaces 10

I tried to upgrade from PrimeFaces 8 to PrimeFaces 10. Everything works fine but I have an error with omega theme :

Grave:   Error Rendering View[/public/main_page.xhtml]
javax.faces.FacesException: Error loading CSS, cannot find "theme.css" resource of "primefaces-omega" library

This is web.xml :

<context-param>
    <param-name>primefaces.THEME</param-name>
    <param-value>omega</param-value>
</context-param>

If I change PrimeFaces version to 8.0, it works fine :

    // This doesn't work
    <dependency>
        <groupId>org.primefaces</groupId>
        <artifactId>primefaces</artifactId>
        <version>10.0.0-RC2</version>
    </dependency>

    // This works
    <dependency>
        <groupId>org.primefaces</groupId>
        <artifactId>primefaces</artifactId>
        <version>8.0</version>
    </dependency>

Do I miss something ?