[Bug] Got error `DataConverter is not set` when receiving an empty value

[roxblnfk]

It seems that #442 is not fully resolved. It works fine with a Untyped Workflow Stub, but not with a regular Stub.

After some recent updates PHP SDK begin to fail on empty array payloads from Golang SDK, while we get EncodedValues their payloads are empty, as such - we don't require DataConverter to decode them.