This type is only used for output response formatting, not for input
validation, so it can be replaced with a basic dict equivalent without
disruption.
This results in fields in WSME types which shouldn't be handled by
WSME because they are already in a dict format. This is handled by
relaxing the validation in the (ex-WSME) types so that a None type
means that WSME shouldn't serialize that attribute. This will allow
old style type serialization to be mixed with plain dicts during the
transition period.
Story: 1651346
Task: 10551
Change-Id: Ifae9bd005fb7cf951b069ade0c92b8d61e095e0f
b1328fa996