public KTableKTableJoinNodeBuilder<K, V1, V2, VR> withValueSerde(final Serde<VR> valueSerde) {
            this.valueSerde = valueSerde;
            return this;
        }
The supplier which provides processor with KTable-KTable join merge functionality.
streams/src/main/java/org/apache/kafka/streams/kstream/internals/graph/KTableKTableJoinNode.java