In GeneralValidatorImpl in resteasy-validation-provider-11 and resteasy-hibernatevalidator-provider, then is a test

try

{ cdiActive = ResteasyCdiExtension.isCDIActive(); }

catch (Exception e)

{ // Intentionally empty. In case ResteasyCdiExtension is not on the classpath. }

to avoid depending on resteasy-cdi. But NoClassDefFoundError is an Error, and doesn't get caught.