Fix tournament population failure when beatmap is not found on server

Author: peppy

osu.Game.Tournament/Models/TournamentBeatmap.cs

@@ -2,7 +2,6 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
-using osu.Framework.Extensions.ObjectExtensions;
 using osu.Game.Beatmaps;
 using osu.Game.Extensions;
 using osu.Game.Online.API.Requests.Responses;
@@ -41,7 +40,7 @@ public TournamentBeatmap(APIBeatmap beatmap)
             StarRating = beatmap.StarRating;
             Metadata = beatmap.Metadata;
             Difficulty = beatmap.Difficulty;
-            Covers = beatmap.BeatmapSet.AsNonNull().Covers;
+            Covers = beatmap.BeatmapSet?.Covers ?? new BeatmapSetOnlineCovers();
         }
 
         public bool Equals(IBeatmapInfo? other) => other is TournamentBeatmap b && this.MatchesOnlineID(b);

osu.Game/Beatmaps/BeatmapSetOnlineCovers.cs

@@ -1,8 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-#nullable disable
-
 using Newtonsoft.Json;
 
 namespace osu.Game.Beatmaps