RE: ERROR ClassPathExplorer getAvailableWidgetSets

These are not really errors in widgetset compilation but Maven interpreting output from an (indirectly) executed class as errors. The topic has also been discussed in other threads.

Ideally, the class outputting those lines should be changed, but other systems (most importantly the Eclipse plugin) depend on that part of the output going to that stream, so the change cannot be done without taking all the interacting systems into account. To complicate the matter further, mixes of old and new versions of the interacting components (Vaadin, Eclipse plugin, Maven plugin and possibly other build systems) will stay in use for a long time.