Changed type parameter T in NavStateSaver to nullable (#1009)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

* **New Features**
  * `NavStateSaver` now supports nullable configuration values.
  * Convenience builders were updated to work with both nullable and non-nullable types, while keeping serialization behavior the same.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: arkivanov

decompose/api/decompose.klib.api

@@ -69,11 +69,6 @@ abstract interface <#A: kotlin/Any, #B: kotlin/Any, #C: kotlin/Any> com.arkivano
     abstract fun navigate(kotlin/Function1<com.arkivanov.decompose.router.panels/Panels<#A, #B, #C>, com.arkivanov.decompose.router.panels/Panels<#A, #B, #C>>, kotlin/Function2<com.arkivanov.decompose.router.panels/Panels<#A, #B, #C>, com.arkivanov.decompose.router.panels/Panels<#A, #B, #C>, kotlin/Unit>) // com.arkivanov.decompose.router.panels/PanelsNavigator.navigate|navigate(kotlin.Function1<com.arkivanov.decompose.router.panels.Panels<1:0,1:1,1:2>,com.arkivanov.decompose.router.panels.Panels<1:0,1:1,1:2>>;kotlin.Function2<com.arkivanov.decompose.router.panels.Panels<1:0,1:1,1:2>,com.arkivanov.decompose.router.panels.Panels<1:0,1:1,1:2>,kotlin.Unit>){}[0]
 }
 
-abstract interface <#A: kotlin/Any> com.arkivanov.decompose.router.children/NavStateSaver { // com.arkivanov.decompose.router.children/NavStateSaver|null[0]
-    abstract fun restoreState(com.arkivanov.essenty.statekeeper/SerializableContainer): #A? // com.arkivanov.decompose.router.children/NavStateSaver.restoreState|restoreState(com.arkivanov.essenty.statekeeper.SerializableContainer){}[0]
-    abstract fun saveState(#A): com.arkivanov.essenty.statekeeper/SerializableContainer? // com.arkivanov.decompose.router.children/NavStateSaver.saveState|saveState(1:0){}[0]
-}
-
 abstract interface <#A: kotlin/Any> com.arkivanov.decompose.router.items/ItemsNavigation : com.arkivanov.decompose.router.children/NavigationSource<com.arkivanov.decompose.router.items/ItemsNavigation.Event<#A>>, com.arkivanov.decompose.router.items/ItemsNavigator<#A> { // com.arkivanov.decompose.router.items/ItemsNavigation|null[0]
     final class <#A1: kotlin/Any> Event { // com.arkivanov.decompose.router.items/ItemsNavigation.Event|null[0]
         constructor <init>(kotlin/Function1<com.arkivanov.decompose.router.items/Items<#A1>, com.arkivanov.decompose.router.items/Items<#A1>>, kotlin/Function2<com.arkivanov.decompose.router.items/Items<#A1>, com.arkivanov.decompose.router.items/Items<#A1>, kotlin/Unit> = ...) // com.arkivanov.decompose.router.items/ItemsNavigation.Event.<init>|<init>(kotlin.Function1<com.arkivanov.decompose.router.items.Items<1:0>,com.arkivanov.decompose.router.items.Items<1:0>>;kotlin.Function2<com.arkivanov.decompose.router.items.Items<1:0>,com.arkivanov.decompose.router.items.Items<1:0>,kotlin.Unit>){}[0]
@@ -157,6 +152,11 @@ abstract interface <#A: kotlin/Any> com.arkivanov.decompose.router.webhistory/We
     }
 }
 
+abstract interface <#A: kotlin/Any?> com.arkivanov.decompose.router.children/NavStateSaver { // com.arkivanov.decompose.router.children/NavStateSaver|null[0]
+    abstract fun restoreState(com.arkivanov.essenty.statekeeper/SerializableContainer): #A? // com.arkivanov.decompose.router.children/NavStateSaver.restoreState|restoreState(com.arkivanov.essenty.statekeeper.SerializableContainer){}[0]
+    abstract fun saveState(#A): com.arkivanov.essenty.statekeeper/SerializableContainer? // com.arkivanov.decompose.router.children/NavStateSaver.saveState|saveState(1:0){}[0]
+}
+
 abstract interface <#A: out kotlin/Any> com.arkivanov.decompose.router.children/ChildNavState { // com.arkivanov.decompose.router.children/ChildNavState|null[0]
     abstract val configuration // com.arkivanov.decompose.router.children/ChildNavState.configuration|{}configuration[0]
         abstract fun <get-configuration>(): #A // com.arkivanov.decompose.router.children/ChildNavState.configuration.<get-configuration>|<get-configuration>(){}[0]
@@ -651,13 +651,13 @@ final fun <#A: kotlin/Any> (com.arkivanov.decompose.value/MutableValue<#A>).com.
 final fun <#A: kotlin/Any> (com.arkivanov.decompose.value/MutableValue<#A>).com.arkivanov.decompose.value/updateAndGet(kotlin/Function1<#A, #A>): #A // com.arkivanov.decompose.value/updateAndGet|updateAndGet@com.arkivanov.decompose.value.MutableValue<0:0>(kotlin.Function1<0:0,0:0>){0§<kotlin.Any>}[0]
 final fun <#A: kotlin/Any> (com.arkivanov.decompose.value/Value<#A>).com.arkivanov.decompose.value/getValue(kotlin/Any?, kotlin.reflect/KProperty<*>): #A // com.arkivanov.decompose.value/getValue|getValue@com.arkivanov.decompose.value.Value<0:0>(kotlin.Any?;kotlin.reflect.KProperty<*>){0§<kotlin.Any>}[0]
 final fun <#A: kotlin/Any> (com.arkivanov.decompose.value/Value<#A>).com.arkivanov.decompose.value/subscribe(com.arkivanov.essenty.lifecycle/Lifecycle, com.arkivanov.decompose.value/ObserveLifecycleMode = ..., kotlin/Function1<#A, kotlin/Unit>) // com.arkivanov.decompose.value/subscribe|subscribe@com.arkivanov.decompose.value.Value<0:0>(com.arkivanov.essenty.lifecycle.Lifecycle;com.arkivanov.decompose.value.ObserveLifecycleMode;kotlin.Function1<0:0,kotlin.Unit>){0§<kotlin.Any>}[0]
-final fun <#A: kotlin/Any> com.arkivanov.decompose.router.children/NavStateSaver(kotlinx.serialization/KSerializer<#A>): com.arkivanov.decompose.router.children/NavStateSaver<#A> // com.arkivanov.decompose.router.children/NavStateSaver|NavStateSaver(kotlinx.serialization.KSerializer<0:0>){0§<kotlin.Any>}[0]
 final fun <#A: kotlin/Any> com.arkivanov.decompose.router.children/transientNavStateSaver(): com.arkivanov.decompose.router.children/NavStateSaver<#A> // com.arkivanov.decompose.router.children/transientNavStateSaver|transientNavStateSaver(){0§<kotlin.Any>}[0]
 final fun <#A: kotlin/Any> com.arkivanov.decompose.router.items/ItemsNavigation(): com.arkivanov.decompose.router.items/ItemsNavigation<#A> // com.arkivanov.decompose.router.items/ItemsNavigation|ItemsNavigation(){0§<kotlin.Any>}[0]
 final fun <#A: kotlin/Any> com.arkivanov.decompose.router.pages/PagesNavigation(): com.arkivanov.decompose.router.pages/PagesNavigation<#A> // com.arkivanov.decompose.router.pages/PagesNavigation|PagesNavigation(){0§<kotlin.Any>}[0]
 final fun <#A: kotlin/Any> com.arkivanov.decompose.router.slot/SlotNavigation(): com.arkivanov.decompose.router.slot/SlotNavigation<#A> // com.arkivanov.decompose.router.slot/SlotNavigation|SlotNavigation(){0§<kotlin.Any>}[0]
 final fun <#A: kotlin/Any> com.arkivanov.decompose.router.stack/StackNavigation(): com.arkivanov.decompose.router.stack/StackNavigation<#A> // com.arkivanov.decompose.router.stack/StackNavigation|StackNavigation(){0§<kotlin.Any>}[0]
 final fun <#A: kotlin/Any> com.arkivanov.decompose.value/MutableValue(#A): com.arkivanov.decompose.value/MutableValue<#A> // com.arkivanov.decompose.value/MutableValue|MutableValue(0:0){0§<kotlin.Any>}[0]
+final fun <#A: kotlin/Any?> com.arkivanov.decompose.router.children/NavStateSaver(kotlinx.serialization/KSerializer<#A!!>): com.arkivanov.decompose.router.children/NavStateSaver<#A> // com.arkivanov.decompose.router.children/NavStateSaver|NavStateSaver(kotlinx.serialization.KSerializer<0:0>){0§<kotlin.Any?>}[0]
 final fun com.arkivanov.decompose.router.pages/getDefaultPageStatus(kotlin/Int, com.arkivanov.decompose.router.pages/Pages<*>): com.arkivanov.decompose.router.children/ChildNavState.Status // com.arkivanov.decompose.router.pages/getDefaultPageStatus|getDefaultPageStatus(kotlin.Int;com.arkivanov.decompose.router.pages.Pages<*>){}[0]
 final inline fun (com.arkivanov.decompose.router.slot/SlotNavigator<*>).com.arkivanov.decompose.router.slot/dismiss(crossinline kotlin/Function1<kotlin/Boolean, kotlin/Unit> = ...) // com.arkivanov.decompose.router.slot/dismiss|dismiss@com.arkivanov.decompose.router.slot.SlotNavigator<*>(kotlin.Function1<kotlin.Boolean,kotlin.Unit>){}[0]
 final inline fun (com.arkivanov.decompose.router.stack/StackNavigator<*>).com.arkivanov.decompose.router.stack/popToFirst(crossinline kotlin/Function1<kotlin/Boolean, kotlin/Unit> = ...) // com.arkivanov.decompose.router.stack/popToFirst|popToFirst@com.arkivanov.decompose.router.stack.StackNavigator<*>(kotlin.Function1<kotlin.Boolean,kotlin.Unit>){}[0]
@@ -678,7 +678,7 @@ final inline fun <#A: kotlin/Any> (com.arkivanov.decompose.router.stack/StackNav
 final inline fun <#A: kotlin/Any> (com.arkivanov.decompose.router.stack/StackNavigator<#A>).com.arkivanov.decompose.router.stack/pushToFront(#A, crossinline kotlin/Function0<kotlin/Unit> = ...) // com.arkivanov.decompose.router.stack/pushToFront|pushToFront@com.arkivanov.decompose.router.stack.StackNavigator<0:0>(0:0;kotlin.Function0<kotlin.Unit>){0§<kotlin.Any>}[0]
 final inline fun <#A: kotlin/Any> (com.arkivanov.decompose.router.stack/StackNavigator<#A>).com.arkivanov.decompose.router.stack/replaceAll(kotlin/Array<out #A>..., crossinline kotlin/Function0<kotlin/Unit> = ...) // com.arkivanov.decompose.router.stack/replaceAll|replaceAll@com.arkivanov.decompose.router.stack.StackNavigator<0:0>(kotlin.Array<out|0:0>...;kotlin.Function0<kotlin.Unit>){0§<kotlin.Any>}[0]
 final inline fun <#A: kotlin/Any> (com.arkivanov.decompose.router.stack/StackNavigator<#A>).com.arkivanov.decompose.router.stack/replaceCurrent(#A, crossinline kotlin/Function0<kotlin/Unit> = ...) // com.arkivanov.decompose.router.stack/replaceCurrent|replaceCurrent@com.arkivanov.decompose.router.stack.StackNavigator<0:0>(0:0;kotlin.Function0<kotlin.Unit>){0§<kotlin.Any>}[0]
-final inline fun <#A: kotlin/Any> com.arkivanov.decompose.router.children/NavStateSaver(crossinline kotlin/Function1<#A, com.arkivanov.essenty.statekeeper/SerializableContainer?>, crossinline kotlin/Function1<com.arkivanov.essenty.statekeeper/SerializableContainer, #A?>): com.arkivanov.decompose.router.children/NavStateSaver<#A> // com.arkivanov.decompose.router.children/NavStateSaver|NavStateSaver(kotlin.Function1<0:0,com.arkivanov.essenty.statekeeper.SerializableContainer?>;kotlin.Function1<com.arkivanov.essenty.statekeeper.SerializableContainer,0:0?>){0§<kotlin.Any>}[0]
+final inline fun <#A: kotlin/Any?> com.arkivanov.decompose.router.children/NavStateSaver(crossinline kotlin/Function1<#A, com.arkivanov.essenty.statekeeper/SerializableContainer?>, crossinline kotlin/Function1<com.arkivanov.essenty.statekeeper/SerializableContainer, #A?>): com.arkivanov.decompose.router.children/NavStateSaver<#A> // com.arkivanov.decompose.router.children/NavStateSaver|NavStateSaver(kotlin.Function1<0:0,com.arkivanov.essenty.statekeeper.SerializableContainer?>;kotlin.Function1<com.arkivanov.essenty.statekeeper.SerializableContainer,0:0?>){0§<kotlin.Any?>}[0]
 
 // Targets: [js, wasmJs]
 final class com.arkivanov.decompose.router.stack.webhistory/DefaultWebHistoryController : com.arkivanov.decompose.router.stack.webhistory/WebHistoryController { // com.arkivanov.decompose.router.stack.webhistory/DefaultWebHistoryController|null[0]

decompose/src/commonMain/kotlin/com/arkivanov/decompose/router/children/NavStateSaver.kt

@@ -9,7 +9,7 @@ import kotlinx.serialization.KSerializer
  * A contract for saving and restoring navigation states.
  */
 @ExperimentalDecomposeApi
-interface NavStateSaver<T : Any> {
+interface NavStateSaver<T> {
 
     /**
      * Saves the provided navigation state into [SerializableContainer].
@@ -33,7 +33,7 @@ interface NavStateSaver<T : Any> {
  * with the provided [save] and [restore] functions.
  */
 @ExperimentalDecomposeApi
-inline fun <T : Any> NavStateSaver(
+inline fun <T> NavStateSaver(
     crossinline save: (T) -> SerializableContainer?,
     crossinline restore: (SerializableContainer) -> T?,
 ): NavStateSaver<T> =
@@ -47,8 +47,12 @@ inline fun <T : Any> NavStateSaver(
  * that saves and restores the navigation state using the provided [serializer].
  */
 @ExperimentalDecomposeApi
-fun <T : Any> NavStateSaver(serializer: KSerializer<T>): NavStateSaver<T> =
+fun <T> NavStateSaver(serializer: KSerializer<T & Any>): NavStateSaver<T> =
     NavStateSaver(
-        save = { SerializableContainer(value = it, strategy = serializer) },
-        restore = { it.consume(strategy = serializer) },
+        save = {
+            SerializableContainer(value = it, strategy = serializer)
+        },
+        restore = {
+            it.consume(strategy = serializer)
+        },
     )