Show an error when the room to leave cannot be found

showLeaveRoomAlert ran its whole body inside client.getRoom(roomId)?.use { }.
When getRoom returned null, which happens for a room the client can no longer
resolve, the body was skipped without writing any state: leaveAction stayed
Uninitialized, so no confirmation dialog and no error was displayed and
Leave room appeared to do nothing at all.

Handle the missing room explicitly and surface it as a failure, which
AsyncActionView already renders with the generic error dialog. leaveRoom used
a !! for the same lookup, so it reported the miss as a NullPointerException;
it now throws the same named exception.

features/leaveroom/impl/src/main/kotlin/io/element/android/features/leaveroom/impl/LeaveRoomPresenter.kt

@@ -60,7 +60,13 @@ class LeaveRoomPresenter(
         roomId: RoomId,
         leaveAction: MutableState<AsyncAction<Unit>>,
     ) = launch(dispatchers.io) {
-        client.getRoom(roomId)?.use { room ->
+        val room = client.getRoom(roomId)
+        if (room == null) {
+            Timber.e("Unable to find room $roomId to leave it")
+            leaveAction.value = AsyncAction.Failure(RoomNotFoundException(roomId))
+            return@launch
+        }
+        room.use {
             val roomInfo = room.roomInfoFlow.first()
             leaveAction.value = when {
                 roomInfo.isDm -> Confirmation.Dm(roomId)
@@ -78,7 +84,8 @@ class LeaveRoomPresenter(
         leaveAction: MutableState<AsyncAction<Unit>>,
     ) = launch(dispatchers.io) {
         leaveAction.runCatchingUpdatingState {
-            client.getRoom(roomId)!!.use { room ->
+            val room = client.getRoom(roomId) ?: throw RoomNotFoundException(roomId)
+            room.use {
                 room
                     .leave()
                     .onSuccess { notificationConversationService.onLeftRoom(client.sessionId, roomId) }
@@ -100,3 +107,5 @@ class LeaveRoomPresenter(
         }
     }
 }
+
+internal class RoomNotFoundException(roomId: RoomId) : IllegalStateException("Room $roomId not found")

features/leaveroom/impl/src/test/kotlin/io/element/android/features/leaveroom/impl/LeaveBaseRoomPresenterTest.kt

@@ -175,6 +175,32 @@ class LeaveBaseRoomPresenterTest {
         }
     }
 
+    @Test
+    fun `present - show error if the room to confirm leaving is not found`() = runTest {
+        val presenter = createLeaveRoomPresenter(client = FakeMatrixClient())
+        presenter.stateFlow().test {
+            val initialState = awaitItem()
+            initialState.eventSink(LeaveRoomEvent.LeaveRoom(A_ROOM_ID, needsConfirmation = true))
+            val errorState = awaitItem()
+            assertThat(errorState.leaveAction).isInstanceOf(AsyncAction.Failure::class.java)
+            cancelAndIgnoreRemainingEvents()
+        }
+    }
+
+    @Test
+    fun `present - show error if the room to leave is not found`() = runTest {
+        val presenter = createLeaveRoomPresenter(client = FakeMatrixClient())
+        presenter.stateFlow().test {
+            val initialState = awaitItem()
+            initialState.eventSink(LeaveRoomEvent.LeaveRoom(A_ROOM_ID, needsConfirmation = false))
+            val progressState = awaitItem()
+            assertThat(progressState.leaveAction).isEqualTo(AsyncAction.Loading)
+            val errorState = awaitItem()
+            assertThat(errorState.leaveAction).isInstanceOf(AsyncAction.Failure::class.java)
+            cancelAndIgnoreRemainingEvents()
+        }
+    }
+
     @Test
     fun `present - reset state after error`() = runTest {
         val presenter = createLeaveRoomPresenter(