In reply to rakesh2learn:
I guess you have the classical setter-no-getters issue here. The set should be done to the agent level typically. I see you are doing at null & * - sort of global name-space. You should be able to debug this quite easily through check_config_settings, see my DVCon US slides @ http://www.go2uvm.org/2016/07/advanced-uvm-tutorial-from-dvcon-us-2016-slides-now-available/
Good Luck
Srini
www.go2uvm.org