c# - Bio metric Device - ZD2F20 -

i need place entity (user/enroll) based data on particular bio metric device (zd2f20). provides properties user , device.

 public enum userproperty         {             username = 0,             enroll = 1,             userextinfo = 2,             accesscontrolsettings = 3,             messages = 4,             privilege = 5,         }  connection.setproperty(userproperty property, object extraproperty, user currentuser, object extradata); e.g.  connection.setproperty(userproperty.enroll, extraproperty, currentuser, null); 

for other properties working fine, enroll property giving me following error object reference not set instance of object.