public Integer mapThrowable(final Throwable throwable) {
        Throwable throwableToCheck = throwable;
        int depthToGo = 20;

        while (true) {
            Integer resId = mapThrowableFlat(throwableToCheck);
            if (resId != null) {
                return resId;
            } else {
                throwableToCheck = throwableToCheck.getCause();
                depthToGo--;
                if (depthToGo <= 0 || throwableToCheck == throwable || throwableToCheck == null) {
                    Logger logger = Logger.Default.get();  // No EventBus instance here
                    logger.log(Level.FINE, "No specific message resource ID found for " + throwable);
                    // return config.defaultErrorMsgId;
                    return null;
                }
            }
        }

    }
Looks at the exception and its causes trying to find an ID.
EventBus/src/org/greenrobot/eventbus/util/ExceptionToResourceMapping.java