Specifying ASYNC option for addjob

[ethul]

I can specify options for addjob that have a corresponding value; e.g.,

client.addjob('queue', 'job', 100, {DELAY: 10}, function(err, res) {
 ...
})

However, I am wondering if there is a way to provide the ASYNC option. I've tried {ASYNC: ''}, but this results in an error. Perhaps in the options function, if the value of the option for a specific key is null or an explicit false then only the key should be added. Also, the result array preallocation should be removed or determined in a different way since some options may not have corresponding values.