@Override
        public String put(@NonNull UUID key, @NonNull String value) {
            String existing = super.put(key, value);

            // check if we need to remove a reverse entry which has been replaced
            // existing might be null
            if (!value.equalsIgnoreCase(existing)) {
                if (existing != null) {
                    this.reverse.remove(existing.toLowerCase(Locale.ROOT), key);
                }
            }

            this.reverse.put(value.toLowerCase(Locale.ROOT), key);
            return existing;
        }
Gets the most recent username used by a given uuid

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