public String toDisplayString(final DisplayType displayType) {
        final Function<UserRef, String> displayTextFunc = NullSafe.requireNonNullElse(
                        displayType, DisplayType.AUTO)
                .getDisplayTextFunc();
        return displayTextFunc.apply(this);
    }
@return "Group" or "User" depending on type.
stroom-util-shared/src/main/java/stroom/util/shared/UserRef.java