In general terms this shows that the natives mechanism is kind of fragile right now.
I can think of two improvements:
When dispatching a native message if there are no method in the native but the method was declared as native in wollok then we should give an specific error message like "method blah() is declared native but not implemented natively !!"
It would be great to have some kind of static check for this. It can be complex because the validator should resolve the native class from the classpath or something.
@javierfernandes says: