public Grouped<K, V> withKeySerde(final Serde<K> keySerde) {
        return new Grouped<>(name, keySerde, valueSerde);
    }
Perform the grouping operation using the provided keySerde for serializing the key.

@param keySerde
       {@link Serde} to use for serializing the key. If {@code null} the default key serde from config will be used

@return a new {@link Grouped} instance configured with the keySerde
streams/src/main/java/org/apache/kafka/streams/kstream/Grouped.java