Null values are improperly serialized

[sproctor]

Data classes with null property values are serialized with those values as a string literal with a value of "null" instead a null literal. Jackson then attempts to de-serialize the string literal to the type of the property.

Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `CustomChildType` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('null')

[uchuhimo]

@sproctor Can you provide a test case for me to reproduce the issue? I will try to fix it.

[sproctor]

Something like:

object ExampleSpec : ConfigSpec {
    val foo by optional(Foo(null))
}

data class Foo(val bar: Bar?)
data class Bar(val baz: String)

I didn't do a lot of digging to see if null values other than data classes cause the issue.

The output from that is:

 {
   "example" : {
     "foo" : {
       "bar" : "null"
     }
   }
 }

It should be:

 {
   "example" : {
     "foo" : {
       "bar" : null
     }
   }
 }

Changing the config file manually fixes the issue until the next time it's saved.

[sproctor]

Sorry, this was way more complicated than necessary. String? exhibits the same behavior.

object ExampleSpec : ConfigSpec {
    val foo by optional<String?>(null)
}

That will store the null with quotes instead of as a null literal. I just didn't notice the issue there because it deserializes to the string "null" instead of a null value, but doesn't cause a crash.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed after 30 days if no further activity occurs, but feel free to re-open a closed issue if needed.