PLAT-6832/6829

- credit missing data field
- in-memory snapshot master  getNamedSnapshot rather than getSnapshot
Disagree, the current impl allows an invalid state to be created. The constructor needs to be corrected rather than maintaining a way to create a broken instance. (note you can create this object fudge encode it and have decode fail  with a validation error on the unset value). IMHO, correctness trumps backwards compatibility in this case.