Cast error on a Kotlin class that extends a Java class

I have a Java project that uses an internal company library made in Kotlin. In this library, I have a Kotlin class that extends the Feign.Builder. This is how the decompiled code looks like

public final class CustomizedFeign public constructor() {
    public final class Builder public constructor() : feign.Feign.Builder {
       ...
    }
}

And this is how the original Kotlin code looks like:

class CustomizedFeign {
    class Builder : Feign.Builder() {
       ... 
    }
}

When I try to cast the CustomizedFeign.Builder class to Feign.Builder in my Java project

final Feign.Builder builder = (Feign.Builder) new CustomizedFeign.Builder();

IntelliJ shows an error: Inconvertible types; cannot cast 'CustomizedFeign.Builder' to 'feign.Feign.Builder'

I don't get why I'm having this error. In java, you can cast from a child class to a parent class without problems. In this case, CustomizedFeign.Builder is a subtype of Feign.Builder, so I should be allowed to cast them... I guess the "Kotlin factor" has something to do with this error.

EDIT: I know I shouldn't need to do an explicit cast. If I don't do it:

final Feign.Builder builder = new CustomizedFeign.Builder();

The error is different but, at the end of the day, the outcome is the same:

Required type:
feign.Feign.Builder
Provided:
CustomizedFeign.Builder

EDIT 2: Somehow I think this is related to trying to do this in a Java project. If I try this code in a Kotlin project, I don't get any error:

val builder: feign.Feign.Builder = CustomizedFeign.Builder()

Copyright License：
Author:「Antamack」,Reproduced under the CC 4.0 BY-SA copyright license with link to original source & disclaimer.
Link to：https://stackoverflow.com/questions/73590893/cast-error-on-a-kotlin-class-that-extends-a-java-class