How to add custom argument while indexing.?

Hi, I want to add an argument load_date for the indexed data. I am trying to do as below, but it is not allowing. Args eventArgs = new Args(); eventArgs.put("load_date", "2016-01-25"); I need to get the events based on date. So, i want to add this argument, so that i could simply match at search time. But i am getting error saying Argument "load_date" is not supported by this handler