Missing group safeguards.

- Server will no longer start up when the guest or default groups cannot
  be located.
- Players joining with unknown groups assigned to them will be
  disconnected with an error

TShockAPI/Commands.cs

@@ -823,10 +823,13 @@ namespace TShockAPI
 						(usingUUID && account.UUID == args.Player.UUID && !TShock.Config.Settings.DisableUUIDLogin &&
 						!String.IsNullOrWhiteSpace(args.Player.UUID)))
 				{
-					args.Player.PlayerData = TShock.CharacterDB.GetPlayerData(args.Player, account.ID);
-
 					var group = TShock.Groups.GetGroupByName(account.Group);
 
+					if (!TShock.Utils.AssertGroupValid(args.Player, group))
+						return;
+
+					args.Player.PlayerData = TShock.CharacterDB.GetPlayerData(args.Player, account.ID);
+
 					args.Player.Group = group;
 					args.Player.tempGroup = null;
 					args.Player.Account = account;

TShockAPI/DB/GroupManager.cs

@@ -202,6 +202,21 @@ namespace TShockAPI.DB
 			Group.DefaultGroup = GetGroupByName(TShock.Config.Settings.DefaultGuestGroupName);
 		}
 
+		internal void EnsureCoreGroupsPresent()
+		{
+			if (!GroupExists(TShock.Config.Settings.DefaultGuestGroupName))
+			{
+				TShock.Log.ConsoleError("The guest group could not be found. This may indicate a typo in the configuration file, or that the group was renamed or deleted.");
+				throw new Exception("The guest group could not be found.");
+			}
+
+			if(!GroupExists(TShock.Config.Settings.DefaultRegistrationGroupName))
+            {
+				TShock.Log.ConsoleError("The default usergroup could not be found. This may indicate a typo in the configuration file, or that the group was renamed or deleted.");
+				throw new Exception("The default usergroup could not be found.");
+            }
+		}
+
 		private void AddDefaultGroup(string name, string parent, string permissions)
 		{
 			if (!GroupExists(name))

TShockAPI/GetDataHandlers.cs

@@ -2450,10 +2450,13 @@ namespace TShockAPI
 						args.Player.State = 2;
 					NetMessage.SendData((int)PacketTypes.WorldInfo, args.Player.Index);
 
-					args.Player.PlayerData = TShock.CharacterDB.GetPlayerData(args.Player, account.ID);
-
 					var group = TShock.Groups.GetGroupByName(account.Group);
 
+					if (!TShock.Utils.AssertGroupValid(args.Player, group))
+						return true;
+
+					args.Player.PlayerData = TShock.CharacterDB.GetPlayerData(args.Player, account.ID);
+
 					args.Player.Group = group;
 					args.Player.tempGroup = null;
 					args.Player.Account = account;
@@ -3004,6 +3007,9 @@ namespace TShockAPI
 
 					var group = TShock.Groups.GetGroupByName(account.Group);
 
+					if (!TShock.Utils.AssertGroupValid(args.Player, group))
+						return true;
+
 					args.Player.Group = group;
 					args.Player.tempGroup = null;
 					args.Player.Account = account;

TShockAPI/TShock.cs

@@ -322,6 +322,7 @@ namespace TShockAPI
 				Regions = new RegionManager(DB);
 				UserAccounts = new UserAccountManager(DB);
 				Groups = new GroupManager(DB);
+				Groups.EnsureCoreGroupsPresent();
 				ProjectileBans = new ProjectileManagager(DB);
 				TileBans = new TileManager(DB);
 				RememberedPos = new RememberedPosManager(DB);

TShockAPI/Utils.cs

@@ -212,6 +212,17 @@ namespace TShockAPI
 			} while (TilePlacementValid(tileX, tileY) && TileSolid(tileX, tileY));
 		}
 
+		public bool AssertGroupValid(TSPlayer player, Group group)
+        {
+			if (group == null)
+			{
+				player.Disconnect("Your account's group could not be found. Please contact server administrators about this.");
+				return false;
+			}
+
+			return true;
+		}
+
 		/// <summary>
 		/// Determines if a tile is valid.
 		/// </summary>

TerrariaServerAPI

@@ -1 +1 @@
-Subproject commit 8c2c087327bbd1f20ff6c46f4d11e5714e57064b
+Subproject commit 4b555bc373dbb470bc69ebed69c79de116f28df2