From e18b524f8e8cd89e94d99d39d324cb0a4d556263 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Wed, 7 Sep 2022 14:08:07 +0900
Subject: [PATCH] Fix missing null checks on `selectedBeatmap` fields in
 `BeatmapCarousel`

---
 osu.Game/Screens/Select/BeatmapCarousel.cs | 30 +++++++++++++++-------
 1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/osu.Game/Screens/Select/BeatmapCarousel.cs b/osu.Game/Screens/Select/BeatmapCarousel.cs
index 3370dfbb4e..e0dfbe2a1c 100644
--- a/osu.Game/Screens/Select/BeatmapCarousel.cs
+++ b/osu.Game/Screens/Select/BeatmapCarousel.cs
@@ -264,8 +264,11 @@ private void beatmapSetsChanged(IRealmCollection<BeatmapSetInfo> sender, ChangeS
             foreach (int i in changes.InsertedIndices)
                 UpdateBeatmapSet(sender[i].Detach());
 
-            if (changes.DeletedIndices.Length > 0)
+            if (changes.DeletedIndices.Length > 0 && SelectedBeatmapInfo != null)
             {
+                // If SelectedBeatmapInfo is non-null, the set should also be non-null.
+                Debug.Assert(SelectedBeatmapSet != null);
+
                 // To handle the beatmap update flow, attempt to track selection changes across delete-insert transactions.
                 // When an update occurs, the previous beatmap set is either soft or hard deleted.
                 // Check if the current selection was potentially deleted by re-querying its validity.
@@ -440,6 +443,9 @@ public void SelectNext(int direction = 1, bool skipDifficulties = true)
 
         private void selectNextSet(int direction, bool skipDifficulties)
         {
+            if (selectedBeatmap == null || selectedBeatmapSet == null)
+                return;
+
             var unfilteredSets = beatmapSets.Where(s => !s.Filtered.Value).ToList();
 
             var nextSet = unfilteredSets[(unfilteredSets.IndexOf(selectedBeatmapSet) + direction + unfilteredSets.Count) % unfilteredSets.Count];
@@ -452,7 +458,7 @@ private void selectNextSet(int direction, bool skipDifficulties)
 
         private void selectNextDifficulty(int direction)
         {
-            if (selectedBeatmap == null)
+            if (selectedBeatmap == null || selectedBeatmapSet == null)
                 return;
 
             var unfilteredDifficulties = selectedBeatmapSet.Items.Where(s => !s.Filtered.Value).ToList();
@@ -481,7 +487,7 @@ public bool SelectNextRandom()
             if (!visibleSets.Any())
                 return false;
 
-            if (selectedBeatmap != null)
+            if (selectedBeatmap != null && selectedBeatmapSet != null)
             {
                 randomSelectedBeatmaps.Push(selectedBeatmap);
 
@@ -524,11 +530,13 @@ public void SelectPreviousRandom()
 
                 if (!beatmap.Filtered.Value)
                 {
-                    if (RandomAlgorithm.Value == RandomSelectAlgorithm.RandomPermutation)
-                        previouslyVisitedRandomSets.Remove(selectedBeatmapSet);
-
                     if (selectedBeatmapSet != null)
+                    {
+                        if (RandomAlgorithm.Value == RandomSelectAlgorithm.RandomPermutation)
+                            previouslyVisitedRandomSets.Remove(selectedBeatmapSet);
+
                         playSpinSample(distanceBetween(beatmap, selectedBeatmapSet));
+                    }
 
                     select(beatmap);
                     break;
@@ -540,9 +548,13 @@ public void SelectPreviousRandom()
 
         private void playSpinSample(double distance)
         {
-            var chan = spinSample.GetChannel();
-            chan.Frequency.Value = 1f + Math.Min(1f, distance / visibleSetsCount);
-            chan.Play();
+            var chan = spinSample?.GetChannel();
+
+            if (chan != null)
+            {
+                chan.Frequency.Value = 1f + Math.Min(1f, distance / visibleSetsCount);
+                chan.Play();
+            }
 
             randomSelectSample?.Play();
         }