GaussianFlux relies on the shape slot, and puts noisy warnings in the logs when the shape slot fails.
However, we probably don't want to add a new flag for GaussianFlux to indicate this failure mode, because it'd be entirely redundant with the shape slot flag. We should figure out some other way to squash this warning - how we do that may depend on whether this is addressed before or after the C++ redesign.
We should also consider having GaussianFlux add an alias to the schema to point back at the shape slot flag, creating what looks like a specific flag for this failure while actually just being a link back to the shape slot flag. That's probably not worth doing within the current C++ interface, however, as it'd require some unpleasant mucking around with ResultMappers.