private String getDisplayNameOrSubjectId(final User user) {
        Objects.requireNonNull(user);
        return Objects.requireNonNullElseGet(user.getDisplayName(), user::getSubjectId);
    }
Get user or group by their UUID.
stroom-security/stroom-security-impl-db/src/main/java/stroom/security/impl/db/UserDaoImpl.java