Ruby on Rails and Redis - cache working intermittent -

i using redis cache data in rails, works first time , caches data after 5 mins expires following error

actionview::template::error (undefined method []' true:trueclass):

this use cache data, custom method monkey patched redis class.

@avg_results = $redis.cache(     :key => "#{current_member.id}-#{@group.id}-avg",     :expire => 300, # seconds, 5 minutes     :timeout => 5  # seconds   )     group.all.to_json   end unless @avg_results.nil?   @avg_results = json.load @avg_results end 

this monkey patch

class redis    def cache(params)     key = params[:key] || raise(":key parameter required!")     expire = params[:expire] || nil     recalculate = params[:recalculate] || nil     expire = params[:expire] || nil     timeout = params[:timeout] || 0     default = params[:default] || nil      if (value = get(key)).nil? || recalculate        begin         value = timeout::timeout(timeout) { yield(self) }       rescue timeout::error         value = default       end        set(key, value)       expire(key, expire) if expire       value     else       value     end   end  end 

so question this, why , getting error actionview::template::error (undefined method []' true:trueclass): ?

edit

i think have tracked issue down memory leak, if server out of memory when redis has expired , saving new data redis true:trueclass set? instead of data database. can patch this? or need track down leak?