protected void onDeserialize(Deserializer buf) {
        // empty
    }
Deserializes the content of this class from the given byte
buffer. This method must be implemented by all subclasses that
have content. If the subclass has no other content than the
semantics of its class type, this method does not need to be
overloaded.

@param buf The buffer to deserialize from.
vespajlib/src/main/java/com/yahoo/vespa/objects/Identifiable.java