IssueTracker

This seems to be still be busted (same error) if you change isNullableAllowed = true (I don't have any errors when changing the same code to isNullableAllowed = false AND <IndividualId>)

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")))
},

Re comment#9 can you please file a new bug? The cause of your issue is different from this one. I'll address your issue in the new bug. Thanks.

Re comment#9 created bug report and cc'd you

I'm also having this issue. I have created a repo for showcasing this: https://github.com/BobbyESP/NavigationParcelablesBugReport

In there you will find another case with a Parcelable object. In my case is quite strange since the logcat shows this error:

Process: com.bobbyesp.navigationbugreport, PID: 23169
                                                                                                    kotlinx.serialization.SerializationException: Serializer for class 'Companion' is not found.
                                                                                                    Please ensure that class is marked as '@Serializable' and that the serialization compiler plugin is applied.
                                                                                                    
                                                                                                    	at kotlinx.serialization.internal.Platform_commonKt.serializerNotRegistered(Platform.common.kt:91)
                                                                                                    	at kotlinx.serialization.SerializersKt__SerializersKt.serializer(Serializers.kt:278)
                                                                                                    	at kotlinx.serialization.SerializersKt.serializer(Unknown Source:1)
                                                                                                    	at androidx.navigation.NavGraph.setStartDestination(NavGraph.kt:404)

Re comment#12, your stacktrace isn't clear which startDestination is causing the issue.

But based on your source code, it is your startDestination in UtilitiesNavigation graph because you are not passing in the song arg for your SongInformationPage.

With safe args, you can conveniently pass in starting arguments by passing in a class instance. The arguments will automatically be available within the starting composable.

This means your nested graph should be

navigation<UtilitiesNavigator>(
       startDestination = SongInformationPage(song = ...),
) 

If your startDestination does not contain arguments, then you can pass in either:

@Serializable 
object MyDestination

startDestination = MyDestination

--- OR ---

@Serializable
class MyDestination

startDestination = MyDestination::class

If you have further questions, please file a separate bug so it is easier for other users with the same question to locate the answer.

comment#15 what's the actual exception message? Can you file a separate bug and attach a sample app?