Implementation: IOperationTransformer class hierarchy used to transform one kind of operation into another; Factory Method design pattern; used in constructors of ClosureOperation and ReadIncOperation; used in BasicProcess.filter_fill() method

Refactor: constructors of BasicObservation class hierarchy to avoid NullPointerException when random distribution throws nothing into a single process in RandomBasicObservationConstructor

Test: avoid NullPointerException when random distribution throws no operations into a single process in RandomBasicObservationConstructor