Add assertions against null reference for connection usages

osu.Game/Online/Multiplayer/OnlineMultiplayerClient.cs

@@ -4,6 +4,7 @@
 #nullable enable
 
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.SignalR.Client;
@@ -79,6 +80,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.FromCanceled<MultiplayerRoom>(new CancellationToken(true));
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync<MultiplayerRoom>(nameof(IMultiplayerServer.JoinRoomWithPassword), roomId, password ?? string.Empty);
         }
 
@@ -87,6 +90,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.FromCanceled(new CancellationToken(true));
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.LeaveRoom));
         }
 
@@ -95,6 +100,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.TransferHost), userId);
         }
 
@@ -103,6 +110,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.KickUser), userId);
         }
 
@@ -111,6 +120,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.ChangeSettings), settings);
         }
 
@@ -119,6 +130,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.ChangeState), newState);
         }
 
@@ -127,6 +140,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.ChangeBeatmapAvailability), newBeatmapAvailability);
         }
 
@@ -135,6 +150,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.ChangeUserMods), newMods);
         }
 
@@ -143,6 +160,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.SendMatchRequest), request);
         }
 
@@ -151,6 +170,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.StartMatch));
         }
 
@@ -159,6 +180,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.AbortGameplay));
         }
 
@@ -167,6 +190,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.AddPlaylistItem), item);
         }
 
@@ -175,6 +200,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.EditPlaylistItem), item);
         }
 
@@ -183,6 +210,8 @@ namespace osu.Game.Online.Multiplayer
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.InvokeAsync(nameof(IMultiplayerServer.RemovePlaylistItem), playlistItemId);
         }
 

osu.Game/Online/Spectator/OnlineSpectatorClient.cs

@@ -3,6 +3,7 @@
 
 #nullable enable
 
+using System.Diagnostics;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.SignalR.Client;
 using osu.Framework.Allocation;
@@ -51,6 +52,8 @@ namespace osu.Game.Online.Spectator
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.SendAsync(nameof(ISpectatorServer.BeginPlaySession), state);
         }
 
@@ -59,6 +62,8 @@ namespace osu.Game.Online.Spectator
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.SendAsync(nameof(ISpectatorServer.SendFrameData), data);
         }
 
@@ -67,6 +72,8 @@ namespace osu.Game.Online.Spectator
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.SendAsync(nameof(ISpectatorServer.EndPlaySession), state);
         }
 
@@ -75,6 +82,8 @@ namespace osu.Game.Online.Spectator
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.SendAsync(nameof(ISpectatorServer.StartWatchingUser), userId);
         }
 
@@ -83,6 +92,8 @@ namespace osu.Game.Online.Spectator
             if (!IsConnected.Value)
                 return Task.CompletedTask;
 
+            Debug.Assert(connection != null);
+
             return connection.SendAsync(nameof(ISpectatorServer.EndWatchingUser), userId);
         }
     }