In case the data is not in the cache any more, the data is lost, and thus an AsapoDataNotInCacheError is mapped to a MissingDataError.
SimpleAsapoReceiver can now also throw a MissingDataError, but this should be ok as a worker either expects this error or it falls back to the defaul no-op handler.
The implementation revealed an error in the testing code, which is now fixed in the first commit.
Closes #10 (closed)