Warning from ASDF

[rpgoldman]

I get this warning loading protobuf-example

; Loading
;    /Users/rpg/projects/gridguard/protobuf-cl/example/protobuf-example.asd
Warning: No dependency propagating scheme specified for operation class
         PROTOBUF-SYSTEM::PROTO-TO-LISP.
The class needs to be updated for ASDF 3.1 and specify appropriate
         propagation mixins.

I believe that this operation needs to be defined as a subclass of ASDF:SELFWARD-OPERATION, but I will have to check.