It seems that NuxeoPrincipalListJsonWriter is not used in automation.
Formerly we used to create Codec for automation. There's AbstractMarshallingRegistryCodec to bridge automation codec with nuxeo-core-io, but there's also a fallback on nuxeo-core-io when no codec/serialiser is found.
A quick fix could be creating the missing Codec.
But as automation codec layer does more or less what nuxeo-core-io does in a more generic way, we should fix how marshaller is retrieved in this case and deprecate codec layer (in another ticket).