How to implement getCause() when implementing AbstractThrowableProblem?

[jehrenzweig-leagueapps]

I'm just getting started with Micronaut (using Kotlin) & am trying to understand how to implement the getCause() function when creating a custom class that implements AbstractThrowableProblem:

class CustomProblemResponseBase : AbstractThrowableProblem(
	URI.create("about:blank"),
	"Unable to process request.",
	HttpStatusType(HttpStatus.UNPROCESSABLE_ENTITY),
	"An error occurred while attempting to process the HTTP request.",
) {
	@JsonIgnore
	override fun getCause(): Exceptional {
		TODO("Not yet implemented")
	}
}

I don't understand why I'm forced to implement getCause() and/or what I should be replacing TODO("Not yet implemenented"). What if there isn't any underlying cause I want to describe -- what would the body of getCause() look like then? It appears I have to return something -- I can't return null.

It's entirely possible I'm missing something about how AbstractThrowableProblem is intended to be used. Any advice is greatly appreciated -- thanks in advance!

[yawkat]

you don't have to override that method

[jehrenzweig-leagueapps]

If I comment out override fun getCause(): Exceptional { ... }, I immediately see the following error in IntelliJ:

Class 'CustomProblemResponseBase' is not abstract and does not implement abstract base class member 
public abstract fun getCause(): Exceptional! defined in org.zalando.problem.AbstractThrowableProblem

[yawkat]

Ah, this is a kotlin issue, see the discussion here zalando/problem#145

[jehrenzweig-leagueapps]

That issue is closed, so it appears I need to override getCause() in my code, even though in my case I'm not interested in overriding the superclass method's behavior. Not ideal, but also not a big deal.

However, I'm still curious if there are any examples around that show how one would override getCause() and what that code would look like. I just want to understand a use case that would mandate writing override code.

[yawkat]

I don't think it makes sense to override getCause for this class (except for the kotlin bug that requires it)

[jehrenzweig-leagueapps]

Ok, good. I'm still curious what type of class / use case would warrant overriding getCause(), and what that method would look like. But at least I have an answer to my original question -- thank you.

[jehrenzweig-leagueapps]

TLDR: There's a Kotlin issue ( zalando/problem#145 ) that requires getCause() be overridden when implementing AbstractThrowableProblem -- even if you want the default behaviour & don't have any need/desire to write your own getCause() implementation.

Unfortunately, the Kotlin ticket was marked closed, so the workaround right now is to replace TODO("Not yet implemented") with super.cause in the body of the overridden getCause() method:

override fun getCause(): Exceptional? = super.cause