I have a bean component implementing a REST service interface binding. Now within the bean there was a NoClassDefFoundError thrown. But in the logfiles it showed up as java.lang.ClassCastException: org.switchyard.HandlerException cannot be cast to java.lang.Boolean because SY tried to map the HandlerException to the boolean return value of the REST function.
Without enabling message tracing there was no mention of the original NoClassDefFoundError anywhere.