Someone else had to work with that turd of WSO2 Enterprise Service Bus?
I hate everything of it: its fucking buggy IDE (a lazy fork of Eclipse in which they didn't even bothered to replace the Eclipse icon), its cryptic XML language which makes basic operations such as accessing a JSON field a complete PITA, its fragility (often syntax errors doesn't get caught by the compiler but causes runtime errors which are hard to diagnose) its shitty testability...