If you are using Object Reference type Property Objects to store references, then there is no need to set those variables to nothing or null. When the variable leaves scope (i.e. when the sequence or execution finishes), TestStand will automatically release the references.
This is one advantage to using the TestStand API from a sequence, you don't have to worry about closing the references, because the Engine will do it for you.
Josh W.
Certified TestStand Architect
Formerly blue