private static String getMessage(Throwable t) {
        String message = t.getMessage();
        if (t.getCause() == null) {
            if (message == null) return t.getClass().getSimpleName();
        } else {
            if (message == null) return null;
            if (message.equals(t.getCause().getClass().getName() + ": " + t.getCause().getMessage())) return null;
        }
        return message;
    }
Returns a useful message from *this* exception, or null if there is nothing useful to return
vespajlib/src/main/java/com/yahoo/yolean/Exceptions.java