maybe worth knowing, I am on kotlin `1.3.21` and t...

# getting-started

[thanksforallthefish]

maybe worth knowing, I am on kotlin 1.3.21 and the base classes are from spring (maybe I can post in spring channel as well, but this seems more generally related to kotlin, spring is relevant only because I have no influence on how enhance is called, it has to accept `null`s)

[Andreas Sinz]

Just a shot in the dark, you could annotate the parameters inside your java class with @Nullable

[thanksforallthefish]

I cannot, HateoasSortHandlerMethodArgumentResolver comes from a library. @Nullable would solve the issue though

[Robert Jaros]

@thanksforallthefish could you write what is happening at runtime?

[thanksforallthefish]

the whole story is this code is used to handle pagination in http requests, thorugh a sort query parameter (which is optional). If no sort parameter is received, the framework (spring-data) calls the enhance method with null. does this answer you?

[thanksforallthefish]

as a temporary solution, I am implementing Blabla in java eh eh

[hho]

I think it is a Spring Problem: The entire package is annotated not nullable: https://github.com/spring-projects/spring-data-commons/blob/master/src/main/java/org/springframework/data/web/package-info.java

That's why the Kotlin compiler won't let you override with nullable types.

[Robert Jaros]

@thanksforallthefish I'm asking what exactly is happening when spring calls this method - if it's an exception could you paste a stacktrace?

[hho]

When Java code calls a Kotlin method with null where the Kotlin parameter is declared non-nullable, a java.lang.IllegalArgumentException: Parameter specified as non-null is null is thrown.

[Robert Jaros]

@hho that method is from UriComponentsContributor from a different package

[Robert Jaros]

no, i'm taking it back

[hho]

yes, but it's overridden

[hho]

i think the spring team just forgot to sprinkle some @Nullable on the parameters.

[hho]

Actually, the UriComponentsContributor interface explicitly states that the parameters can never be null. So the annotations seem correct.

[hho]

The question is then: Why does the framework call that method with `null`…

[Robert Jaros]

any idea which parameter is null ?

[thanksforallthefish]

sorry, meetings here. anyway, the parameter value is nullable (https://github.com/spring-projects/spring-hateoas/blob/master/src/main/java/org/springframework/hateoas/server/mvc/UriComponentsContributor.java#L46), so I guess it is indeed a problem with spring data commons declaring the base class override (HateoasSortHandlerMethodArgumentResolver) non nullable

[hho]

I created https://jira.spring.io/browse/DATACMNS-1486

[thanksforallthefish]

glad you shared, I was a couple of minutes away of pressing the create issue button

[hho]

I also opened https://github.com/spring-projects/spring-data-commons/pull/341