Bugfix: Worker.all should never return nil

Author: nirvdrum

lib/resque/worker.rb

@@ -24,7 +24,7 @@ class Worker
 
     # Returns an array of all worker objects.
     def self.all
-      Array(redis.smembers(:workers)).map { |id| find(id) }
+      Array(redis.smembers(:workers)).map { |id| find(id) }.compact
     end
 
     # Returns an array of all worker objects currently processing