It implies that the document has no locales - if the document *does* have locales, then they are always set on the context by the `AutoRouteManager`).

Maybe it would suffice to add a hint: "..., maybe this document is not translatable?"

This is currently a runtime exception.. we could, technically, validate this in the DIC I guess, but then it *seems* more trouble than it is worth, and conflicts with switching over to `jms/metadata` (if we choose to go down that road).