From JBEAP-9423:

RESTEasy implementation of Base64 class uses printStackTrace method, but this method shouldn't be used. PrintStackTrace is used in public decode method, this method can be used in deployments.

https://github.com/resteasy/Resteasy/blob/master/resteasy-jaxrs/src/main/java/org/jboss/resteasy/util/Base64.java#L1391