I'm using the Ktable's foreign key join (ref: KIP-213). When I try to leftJoin two KTables, and the left side's foreignKey does not have a key match in the right (other) KTable, the Join operation invokes the serializer with a foreignValue=null. This then causes a NullPointerException in the provided (my) serializer.
Stack Trace is attached. Notes:
This foreignValue is passed to Serializer.java#serialize() as 'data'. Ultimately, it ends up in SubscriptionResponseWrapperSerde#serialize (#72) where 'serliazedData` is null. This is what is passed to my serializer.
This exception is readily reproducible; just set up the left message-value to include a foreign key value that does not exist on the right side (the 'other' table).