Feature Request: built in Java8 Optional support for execution methods

A lot of the execution methods would really benefit from having built in Optional support.

Allowing more customized control to throw specific errors without having to handle NPEs.

A lot of times there is running execution.getVariable("…").toString(), and being able to get a built in Optional would help to clean up some of the code!

(yes we can using Optional.ofNullable()), but having the built in methods really makes things nicer to work with now that Java8 is the standard.