What happens when an @Duck procedure returns a type but that type can't be found?

[dwtj]

@paninij currently gives a compile error such as this:

A capsule core has a procedure whose return type cannot be ducked. Cannot duck type `MyMissingType` because it has TypeKind ERROR.

Then subsequent capsule generation is not performed. This is annoying for an @paninij developer. This type may be generated by some other annotation processor in this round or in a later round of processing. The developer may also have just made a typo. In the former case, we are reporting an error where there is none. In the latter case, we are very noisily and cryptically announcing a missing type; @paninij should not be doing this: the normal Java compiler checks should be doing this.