EndpointHelper.resolveReferenceListParameter can sometimes return immutable lists, which can cause issues when other components try to add items to those lists.
The fact that other endpoints (like jetty-common JettyHttpComponent [enableCors line 279]) can add other components into the lists can cause hard to track down failures.
Sorry don't have a patch file, but the lines i would fix in EndpointHelper.java would be:
line 350: return Collections.emptyList();
line 360: return Arrays.asList(elements.size())
These should just return ArrayLists.
I know these parameters should optionally be Lists already, and this is a slight performance hit when starting up, but i think it's better than trying to figure out what went wrong when it fails.
My particular scenario was a Jetty endpoint with a filtersRef (with a single Filter - not a list) and then enableCORS=true. The filtersRef returned Arrays.asLIst and then enableCORS tried to add an element into that list and crashed.