IssueTracker

Reproducible on calling NavBackStackEntry.toRoute().

Example:

Custom Class

@JvmInline
@Serializable
value class IndividualId(val value: String)

NavType for nullable:

val IndividualIdNullableNavType = object : NavType<IndividualId?>(
    isNullableAllowed = true
) {
    override fun get(bundle: Bundle, key: String): IndividualId? = bundle.getString(key)?.let { IndividualId(it) }
    override fun put(bundle: Bundle, key: String, value: IndividualId?) {
        value?.let { bundle.putString(key, it.value) }
    }
    override fun parseValue(value: String): IndividualId? {
        if (value == "null") return null
        return Json.decodeFromString<IndividualId>(value)
    }
    override fun serializeAsValue(value: IndividualId?): String = value?.let { Json.encodeToString(IndividualId.serializer(), it) } ?: ""
}

NavHost code:

composable<IndividualEditRoute>(mapOf(
    typeOf<IndividualId?>() to IndividualIdNullableNavType,
)) { backStackEntry ->
    Log.w("TEST", "Before") // prints
    val individualEditRoute = backStackEntry.toRoute<IndividualEditRoute>()
    Log.w("TEST", "After: individualEditRoute == $individualEditRoute") // never gets here because: ClassCastException: IndividualId cannot be cast to java.lang.String
    IndividualEditScreen(navController)
}

The following works (no error):

onClick = {
    navController.navigate(IndividualEditRoute())
},

The following will cause a "ClassCastException: IndividualId cannot be cast to java.lang.String"

onClick = {
    navController.navigate(IndividualEditRoute(IndividualId("123")))
},