Class Twitter::NotModifiedError
In: lib/twitter/core.rb
Parent: RESTError

Runtime error leaf class raised when Twitter.com API has no new results to return from the last query. HTTP code: 304 (aka Not Modified).

To handle specifically you would do the following:

 begin
   timeline = twitter.timeline_for(:friends, :since => tweet)
 rescue NotModifiedError => nme
   timeline = []
 end

[Validate]