public boolean isWhiteListed(K key) {
        return key != null && whitelist.contains(key);
    }
Checks whether the given key is whitelisted, meaning corresponding entry can
be changed even the map is freezed.

@param key non-null key
@return true if the key is whitelisted; false otherwise
clickhouse-data/src/main/java/com/clickhouse/data/ClickHouseFreezableMap.java