def fetch(id)
      return nil unless exists?(id)
      cached(id) { klass.from_url(get(id), prefix) }
    end
def fetch(id)
      return nil unless exists?(id)
      cached(id) { klass.from_url(get(id), prefix) }
    end
Fetch a specific resource in the collection by id.

 @example Fetch a resource
   Bacon.first.items.fetch('crispy')

 @param [String, Symbol] id
   the id of the resource to fetch

 @return [Resource::Base, nil]
   the fetched class, or nil if it does not exists