How do you make Jackson use Kotlin default params for missing values?

I've a Kotlin data class that looks like this,

data class SomeData(
   private val notInJson: String = "some default value",
   private val inJson: String
)

and a json string, I wish to deserialize into an instance of this class -

{
    "inJson" : "value"
}

When I try to deserialize this data, I get an error that the parameter notInJson cannot be null. Seems like Jackson is passing a null value for it since it's missing in the json string.

Is there a way to have Jackson not pass in any value for it, so that the default specified in the class definition could be used?

--EDIT--

I do register a KotlinModule() with the mapper. Using version 2.7.8 or all jackson packages involved.

The following code -

@Test fun jackson_kotlin_module() {
    val mapper = ObjectMapper().registerModule(KotlinModule())
    println(
        mapper.readValue("""{ "inJson" : "some value" }""",     SomeData::class.java))
}

gives me -

com.fasterxml.jackson.databind.JsonMappingException: Instantiation of [simple 
type, class SomeData] value failed (java.lang.IllegalArgumentException): 
Parameter specified as non-null is null: method SomeData.<init>, parameter 
notInJson
at [Source: { "inJson" : "some value" }; line: 1, column: 27]

Solution

Default params is a Kotlin feature. Jackson does not know about it hence we need to inform it somehow to be able to support it. Thankfully there's the excellent jackson-module-kotlin which let's you do:

val mapper: ObjectMapper = ObjectMapper()
        .registerKotlinModule() //let Jackson know about Kotlin via extension method
...
data class SomeData(
    private val notInJson: String = "some default value",
    private val inJson: String
)
...
val data = mapper.readValue<SomeData>("""{"inJson": "sample value"}""")
println(data) // -> SomeData(notInJson=some default value, inJson=sample value)

For instructions how to use it take a look at jackson-module-kotlin Readme and pay special attention to versions of the module and Jackson itself. In order for the default parameters to work you need at least version 2.8.4 of jackson-module-kotlin