[css3-mediaqueries] Should "@media { … }" be valid?

Example VII from latest revision of CSS3 Media Queries spec says that
following two rules are equivalent:

    @media all { … }
    @media { … }

However, the second rule does not follow the grammar as there must be
at least one media_type or expression is media query:

    media_query
     : [ONLY | NOT]? S* media_type S* [ AND S* expression ]*
     | expression [ AND S* expression ]*

So, is this an error in the grammar or should such rule be really
treated as invalid by parsers?

Cheers,
Jarek Foksa