for example, https://github.com/apache/kafka/blob/trunk/streams/streams-scala/src/main/scala/org/apache/kafka/streams/scala/Serdes.scala#L28 invokes Serdes.String() once and caches the result.
However, the implementation of the String serde has a non-empty configure method that is variant in whether it's used as a key or value serde. So we won't get correct execution if we create one serde and use it for both keys and values.
The fix is simple: change all the `val` declarations in scala.Serdes to `def`. Thanks to the referential transparency for parameterless methods in scala, no user-facing code will break.