Fixed handling of invalid roles

src/Discord.Net/DiscordSocketClient.cs

@@ -114,6 +114,11 @@ namespace Discord
 #endif
 
             _serializer = new JsonSerializer { ContractResolver = new DiscordContractResolver() };
+            _serializer.Error += (s, e) =>
+            {
+                _gatewayLogger.WarningAsync(e.ErrorContext.Error).GetAwaiter().GetResult();
+                e.ErrorContext.Handled = true;
+            };
             
             ApiClient.SentGatewayMessage += async opCode => await _gatewayLogger.DebugAsync($"Sent {(GatewayOpCode)opCode}").ConfigureAwait(false);
             ApiClient.ReceivedGatewayEvent += ProcessMessageAsync;

src/Discord.Net/Entities/Users/GuildUser.cs

@@ -62,7 +62,11 @@ namespace Discord
                 var roles = ImmutableArray.CreateBuilder<Role>(value.Length + 1);
                 roles.Add(Guild.EveryoneRole);
                 for (int i = 0; i < value.Length; i++)
-                    roles.Add(Guild.GetRole(value[i]));
+                {
+                    var role = Guild.GetRole(value[i]);
+                    if (role != null)
+                        roles.Add(role);
+                }
                 Roles = roles.ToImmutable();
                 GuildPermissions = new GuildPermissions(Permissions.ResolveGuild(this));
             }