 			exists = parseInt exists
 			if exists == 1
 				metrics.inc "doc-blocking"
-				callback err, false
+				callback null, false
 			else
 				metrics.inc "doc-not-blocking"
-				callback err, true
+				callback null, true
 
 	releaseLock: (doc_id, lockValue, callback)->
 		key = keys.blockingKey(doc_id:doc_id)

						return callback(err) if err? # error freeing lock
						callback null, false # tell caller they didn't get the lock
				else
					callback err, true, lockValue
			else
				metrics.inc "doc-blocking"
				profile.log("doc is locked").end()
				callback err, false

	getLock: (doc_id, callback = (error, lockValue) ->) ->
		startTime = Date.now()

				return callback(new Error("tried to release timed out lock"))
			else
				profile.log("unlockScript:ok").end()
				callback(null,result)
