Github user GJL commented on the issue:
https://github.com/apache/flink/pull/5573
@yanghua Take a look at `SerializedValueDeserializer` and
`SerializedValueSerializer`. You can use `@JsonSerialize(using= ... )`,
`@JsonSerialize(keyUsing= ... )`, and `@JsonDeserialize` to specify the class
for ser/des.---
