Hi,
We would like to extend SingleEventUpcaster and wrap several of these in an EventUpcasterChain. But we do not see how, because SingleEventUpcaster extends SingleEntryUpcaster, while the constructor of SingleEntryUpcaster takes instances of EventUpcaster. Have we missed something or is it possible we have stumbled on a bug. 
Regards,
Hi Eric,
You have indeed stumbled on a bug. Thanks for reporting! A fix for this has already been pushed to the repository (see commit https://github.com/AxonFramework/AxonFramework/commit/fb07614055d3f947a3f746963e0d3cbc1343dbeb).
Meanwhile there’s an easy workaround until the next (minor) version update of the framework. Either create an (abstract) subclass of SingleEventUpcaster that implements EventUpcaster and have your own upcaster implementations extend from that, or just add “implements EventUpcaster” to all your subclasses.
Regards,
Rene