Filter to quickly return empty data by looking into a cached last contents' (pages')
last updated timestamp built by listening to page update event and comment events
There is no login or permission check to make it as fast as possible (no binding to DB conn or querying)
so it will leak content ids and their last update timestamp, as they are not sensitive data so it is not
a security issue. However the class should be kept as is without adding any extra information to the returned JSON
string like page titles.