If a service reference is not found in SCAInvoker, it spits out an NPE from this line:
https://github.com/jboss-switchyard/components/blob/master/sca/src/main/java/org/switchyard/component/sca/SCAInvoker.java#L90

We need to add a conditional to screen for ref == null after this call:
https://github.com/jboss-switchyard/components/blob/master/sca/src/main/java/org/switchyard/component/sca/SCAInvoker.java#L88

If it's null, SCAInvoker should throw a HandlerException with a message like:

"Service reference " + serviceName + " not found in domain " + exchange.getProvider().getDomain().getName()