"isA" has a similar semantics to "instanceof", but works with combinations of traitable beans, trait proxies and trait classes.
Currently, it does not work reliably when the left operand is a non-trait(able) object. It may try to access the internal trait data structures, which are not present, potentially throwing exceptions.
For these cases, "isA" should not try to resolve trait types, but should fall
back to the standard java "instanceof" operator.