Injections that fail when an observer method is invoked are massively hard to track down. Here's the information you get:

org.jboss.weld.exceptions.IllegalArgumentException: WELD-001324 Argument bean must not be null
at org.jboss.weld.manager.BeanManagerImpl.getReference(BeanManagerImpl.java:714)
at org.jboss.seam.exception.control.HandlerMethodImpl.notify(HandlerMethodImpl.java:187)
at org.jboss.seam.exception.control.ExceptionHandlerDispatch.executeHandlers(ExceptionHandlerDispatch.java:128)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.jboss.weld.util.reflection.SecureReflections$13.work(SecureReflections.java:305)
at org.jboss.weld.util.reflection.SecureReflectionAccess.run(SecureReflectionAccess.java:54)
at org.jboss.weld.util.reflection.SecureReflectionAccess.runAsInvocation(SecureReflectionAccess.java:163)
at org.jboss.weld.util.reflection.SecureReflections.invoke(SecureReflections.java:299)
at org.jboss.weld.introspector.jlr.WeldMethodImpl.invokeOnInstance(WeldMethodImpl.java:188)
at org.jboss.weld.introspector.ForwardingWeldMethod.invokeOnInstance(ForwardingWeldMethod.java:59)
at org.jboss.weld.injection.MethodInjectionPoint.invokeOnInstanceWithSpecialValue(MethodInjectionPoint.java:198)
at org.jboss.weld.event.ObserverMethodImpl.sendEvent(ObserverMethodImpl.java:270)
at org.jboss.weld.event.ObserverMethodImpl.sendEvent(ObserverMethodImpl.java:253)
at org.jboss.weld.event.ObserverMethodImpl.notify(ObserverMethodImpl.java:222)
at org.jboss.weld.manager.BeanManagerImpl.notifyObservers(BeanManagerImpl.java:632)
at org.jboss.weld.manager.BeanManagerImpl.fireEvent(BeanManagerImpl.java:619)
at org.jboss.weld.manager.BeanManagerImpl.fireEvent(BeanManagerImpl.java:613)

I expect to see the type and qualifiers at the failing injection point.