From 1d67746d32e43eae2e5cd1946ed116415e260da7 Mon Sep 17 00:00:00 2001
From: Aergwyn <aergwyn@t-online.de>
Date: Sat, 23 Dec 2017 12:53:11 +0100
Subject: [PATCH] fix crash in SongSelect when traversing while zero beatmaps
 are loaded

---
 .../Visual/TestCaseBeatmapCarousel.cs         | 19 ++++++++++++++++++-
 osu.Game/Screens/Select/BeatmapCarousel.cs    |  3 +++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/osu.Game.Tests/Visual/TestCaseBeatmapCarousel.cs b/osu.Game.Tests/Visual/TestCaseBeatmapCarousel.cs
index 66af72dad9..639befef74 100644
--- a/osu.Game.Tests/Visual/TestCaseBeatmapCarousel.cs
+++ b/osu.Game.Tests/Visual/TestCaseBeatmapCarousel.cs
@@ -69,6 +69,7 @@ namespace osu.Game.Tests.Visual
             testSorting();
 
             testRemoveAll();
+            testEmptyTraversal();
         }
 
         private void ensureRandomFetchSuccess() =>
@@ -103,6 +104,8 @@ namespace osu.Game.Tests.Visual
             AddAssert($"{count} {(diff ? "diffs" : "sets")} visible", () =>
                 carousel.Items.Count(s => (diff ? s.Item is CarouselBeatmap : s.Item is CarouselBeatmapSet) && s.Item.Visible) == count);
 
+        private void checkNoSelection() => AddAssert("Selection is null", () => currentSelection == null);
+
         private void nextRandom() =>
             AddStep("select random next", () =>
             {
@@ -274,9 +277,23 @@ namespace osu.Game.Tests.Visual
                 return false;
             }, "Remove all");
 
-            AddAssert("Selection is null", () => currentSelection == null);
+            checkNoSelection();
         }
 
+        private void testEmptyTraversal()
+        {
+            advanceSelection(direction: 1, diff: false);
+            checkNoSelection();
+
+            advanceSelection(direction: 1, diff: true);
+            checkNoSelection();
+
+            advanceSelection(direction: -1, diff: false);
+            checkNoSelection();
+
+            advanceSelection(direction: -1, diff: true);
+            checkNoSelection();
+        }
 
         private BeatmapSetInfo createTestBeatmapSet(int i)
         {
diff --git a/osu.Game/Screens/Select/BeatmapCarousel.cs b/osu.Game/Screens/Select/BeatmapCarousel.cs
index ff1dd95eac..be176c1459 100644
--- a/osu.Game/Screens/Select/BeatmapCarousel.cs
+++ b/osu.Game/Screens/Select/BeatmapCarousel.cs
@@ -181,6 +181,9 @@ namespace osu.Game.Screens.Select
         /// <param name="skipDifficulties">Whether to skip individual difficulties and only increment over full groups.</param>
         public void SelectNext(int direction = 1, bool skipDifficulties = true)
         {
+            if (!Items.Any())
+                return;
+
             int originalIndex = Items.IndexOf(selectedBeatmap?.Drawables.First());
             int currentIndex = originalIndex;