set Beatmap.BeatmapSet to BeatmapSet property in SoloScoreInfo

osu.Game/Online/API/Requests/Responses/SoloScoreInfo.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using JetBrains.Annotations;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Converters;
 using osu.Game.Beatmaps;
@@ -86,7 +87,19 @@ namespace osu.Game.Online.API.Requests.Responses
         public APIBeatmap? Beatmap { get; set; }
 
         [JsonProperty("beatmapset")]
-        public APIBeatmapSet? BeatmapSet { get; set; }
+        [CanBeNull]
+        public APIBeatmapSet BeatmapSet
+        {
+            set
+            {
+                // in the deserialisation case we need to ferry this data across.
+                // the order of properties returned by the API guarantees that the beatmap is populated by this point.
+                if (!(Beatmap is APIBeatmap apiBeatmap))
+                    throw new InvalidOperationException("Beatmap set metadata arrived before beatmap metadata in response");
+
+                apiBeatmap.BeatmapSet = value;
+            }
+        }
 
         [JsonProperty("pp")]
         public double? PP { get; set; }