🧠 TL;DR:

If you’re using sealed interface + object in Kotlin and constructing a static listOf(...) from those objects — beware.
One of your objects might silently be null— if it wasn’t accessed before the list was created. 🤯

🐛 The Bug

I had this clean sealed interface setup:

internal sealed interface StaffRoleOption {
    object Partner : StaffRoleOption
    object Salesman : StaffRoleOption
    object StockManager : StaffRoleOption
    object DeliveryBoy : StaffRoleOption

    companion object {
        val values = listOf(Partner, Salesman, StockManager, DeliveryBoy)
    }
}

Looked fine. Worked great… until it didn’t.
In my RecyclerView adapter:

StaffRoleOption.values[position]  // 😵 Partner was null

Debugging showed this:

values = [null, Salesman, StockManager, DeliveryBoy]

Wait… what? Partner was null?

🤯 Root Cause: Kotlin object is Lazy

Kotlin object declarations are lazily initialized — they only come alive when referenced.
So if Partner wasn’t accessed before values was initialized, it stayed null.

And listOf(...) evaluated the reference — not the live object — which means you’re storing null.

✅ The Fix

💡 Wrap your list in a function to defer resolution until runtime:

companion object {
    fun values(): List<StaffRoleOption> = listOf(Partner, Salesman, StockManager, DeliveryBoy)
}

// Then access it like:
StaffRoleOption.values()[position] // Boom — no more phantom nulls. 🎯

This article was previously published on proandroiddev.com.