Look into dropping Optional from serialized data

[keith-turner]

Optional is used in some of the Recipes APIs. It also used internally. This results in slightly larger serialized data. We could drop the use of Optional internally in classes private instance var. For example DifferenceExport.java line 49 uses Optional internally.

[jkosh44]

Is this still valid? The only place I see Optional being used as a field is in org.apache.fluo.recipes.core.combine.ChangeImpl and org.apache.fluo.recipes.core.map.Update.

[keith-turner]

Is this still valid?

I think its stilll valid in that it would reduce data size. However looking at this now I am wondering what the impact on currently persisted data would be and how to mitigate any negative consequences.