@Override
    public String toString() {
        return "KeyValue(" + key + ", " + value + ")";
    }
Create a new key-value pair.

@param key   the key
@param value the value
@param <K>   the type of the key
@param <V>   the type of the value
@return a new key-value pair
streams/src/main/java/org/apache/kafka/streams/KeyValue.java