Affects: 5.3.2

Having both Jackson and kotlinx.serialization in the classpath, kotlinx.serialization will try to deserialize Java interfaces implemented by Java classes resulting in the following exception:

org.springframework.http.converter.HttpMessageNotReadableException: Could not read JSON: Polymorphic serializer was not found for missing class discriminator ('null') ... nested exception is kotlinx.serialization.json.internal.JsonDecodingException: Polymorphic serializer was not found for missing class discriminator ('null') 

The issue comes from the KotlinSerializationJsonHttpMessageConverter.candRead() method that returns true when the Type is a Java interface.

In case of Java concrete implementations, this method should return false and let Jackson handle the conversion.