Make remaining model classes nullable and serializable

osu.Game/Online/RealtimeMultiplayer/MultiplayerClientState.cs

@@ -1,6 +1,8 @@
 // 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 enable
+
 namespace osu.Game.Online.RealtimeMultiplayer
 {
     public class MultiplayerClientState

osu.Game/Online/RealtimeMultiplayer/MultiplayerRoom.cs

@@ -1,6 +1,8 @@
 // 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 enable
+
 using System;
 using System.Collections.Generic;
 
@@ -25,13 +27,18 @@ namespace osu.Game.Online.RealtimeMultiplayer
         /// <summary>
         /// All currently enforced game settings for this room.
         /// </summary>
-        public MultiplayerRoomSettings Settings { get; set; }
+        public MultiplayerRoomSettings Settings { get; set; } = MultiplayerRoomSettings.Empty();
 
         /// <summary>
         /// All users currently in this room.
         /// </summary>
         public List<MultiplayerRoomUser> Users { get; set; } = new List<MultiplayerRoomUser>();
 
+        /// <summary>
+        /// The host of this room, in control of changing room settings.
+        /// </summary>
+        public MultiplayerRoomUser? Host { get; set; }
+
         private object writeLock = new object();
 
         /// <summary>

osu.Game/Online/RealtimeMultiplayer/MultiplayerRoomSettings.cs

@@ -1,6 +1,8 @@
 // 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 enable
+
 using System;
 using System.Collections.Generic;
 using System.Linq;
@@ -9,6 +11,7 @@ using osu.Game.Online.API;
 
 namespace osu.Game.Online.RealtimeMultiplayer
 {
+    [Serializable]
     public class MultiplayerRoomSettings : IEquatable<MultiplayerRoomSettings>
     {
         public int? BeatmapID { get; set; }
@@ -18,8 +21,10 @@ namespace osu.Game.Online.RealtimeMultiplayer
         [NotNull]
         public IEnumerable<APIMod> Mods { get; set; } = Enumerable.Empty<APIMod>();
 
-        public bool Equals(MultiplayerRoomSettings other) => BeatmapID == other?.BeatmapID && Mods.SequenceEqual(other?.Mods) && RulesetID == other?.RulesetID;
+        public bool Equals(MultiplayerRoomSettings other) => BeatmapID == other.BeatmapID && Mods.SequenceEqual(other.Mods) && RulesetID == other.RulesetID;
 
         public override string ToString() => $"Beatmap:{BeatmapID} Mods:{string.Join(',', Mods)} Ruleset:{RulesetID}";
+
+        public static MultiplayerRoomSettings Empty() => new MultiplayerRoomSettings();
     }
 }

osu.Game/Online/RealtimeMultiplayer/MultiplayerRoomState.cs

@@ -1,6 +1,8 @@
 // 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 enable
+
 namespace osu.Game.Online.RealtimeMultiplayer
 {
     /// <summary>

osu.Game/Online/RealtimeMultiplayer/MultiplayerRoomUser.cs

@@ -1,27 +1,29 @@
 // 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 enable
+
 using System;
 using osu.Game.Users;
 
 namespace osu.Game.Online.RealtimeMultiplayer
 {
+    [Serializable]
     public class MultiplayerRoomUser : IEquatable<MultiplayerRoomUser>
     {
+        public readonly long UserID;
+
+        public MultiplayerUserState State { get; set; } = MultiplayerUserState.Idle;
+
+        public User? User { get; set; }
+
         public MultiplayerRoomUser(in int userId)
         {
             UserID = userId;
         }
 
-        public long UserID { get; }
-
-        public MultiplayerUserState State { get; set; }
-
-        public User User { get; set; }
-
         public bool Equals(MultiplayerRoomUser other)
         {
-            if (ReferenceEquals(null, other)) return false;
             if (ReferenceEquals(this, other)) return true;
 
             return UserID == other.UserID;
@@ -29,9 +31,8 @@ namespace osu.Game.Online.RealtimeMultiplayer
 
         public override bool Equals(object obj)
         {
-            if (ReferenceEquals(null, obj)) return false;
             if (ReferenceEquals(this, obj)) return true;
-            if (obj.GetType() != this.GetType()) return false;
+            if (obj.GetType() != GetType()) return false;
 
             return Equals((MultiplayerRoomUser)obj);
         }