The problem is that initialization of Accept class does not actually happen, and the delegate field is null.
The RuntimeDelegate is an interface whose implementation should be specified in META-INF/service/javax.ws.rs.ext.RuntimeDelegate file which is searched on the class path.
wink-common.jar contains such a service file with the correct class name of the implementation but if some other service file with the same name is found on class path (on of the jars) before the correct one, we will have such a weird behavior.