The current site definition has menu items defined as

    <menu ref="modules" collapse="false" inherit="top"/>
    <menu ref="parent" collapse="false" inherit="top"/>
    <menu ref="reports" collapse="false" inherit="top"/>
  

– the collapse attribute is not defined; not sure where we got this from, possibly so old/early version of Maven or the site plugin. We can get rid of it, it doesn't seem to have any effect, and newer versions of the site plugin won't allow it.