public @Nullable UUID lookupUuid(String username) {
        Set<UUID> uuids = this.lookupMap.lookupUuid(username);
        return Iterables.getFirst(uuids, null);
    }
Gets the most recent uuid which connected with the given username, or null

@param username the username to lookup with
@return a uuid, or null
common/src/main/java/me/lucko/luckperms/common/storage/implementation/file/FileUuidCache.java