Fix IllegalArgumentException occurring when using /de back

[dmccoystephenson]

org.bukkit.command.CommandException: Unhandled exception executing command 'de' in plugin DansEssentials v2.2
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:47) ~[spigot-api-1.18.2-R0.1-SNAPSHOT.jar:?]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:149) ~[spigot-api-1.18.2-R0.1-SNAPSHOT.jar:?]
at org.bukkit.craftbukkit.v1_18_R2.CraftServer.dispatchCommand(CraftServer.java:826) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.network.PlayerConnection.a(PlayerConnection.java:1957) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.network.PlayerConnection.a(PlayerConnection.java:1796) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.network.PlayerConnection.a(PlayerConnection.java:1777) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.network.protocol.game.PacketPlayInChat.a(PacketPlayInChat.java:46) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.network.protocol.game.PacketPlayInChat.a(PacketPlayInChat.java:1) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.network.protocol.PlayerConnectionUtils.lambda$0(PlayerConnectionUtils.java:31) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.TickTask.run(SourceFile:18) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.util.thread.IAsyncTaskHandler.d(SourceFile:157) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.util.thread.IAsyncTaskHandlerReentrant.d(SourceFile:23) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.b(MinecraftServer.java:1190) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.d(MinecraftServer.java:1) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.util.thread.IAsyncTaskHandler.y(SourceFile:131) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.be(MinecraftServer.java:1169) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.y(MinecraftServer.java:1162) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.util.thread.IAsyncTaskHandler.c(SourceFile:140) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.x(MinecraftServer.java:1146) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:1051) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at net.minecraft.server.MinecraftServer.lambda$0(MinecraftServer.java:304) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at java.lang.Thread.run(Thread.java:833) [?:?]
Caused by: java.lang.IllegalArgumentException: location
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:145) ~[guava-31.0.1-jre.jar:?]
at org.bukkit.craftbukkit.v1_18_R2.entity.CraftPlayer.teleport(CraftPlayer.java:778) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at org.bukkit.craftbukkit.v1_18_R2.entity.CraftEntity.teleport(CraftEntity.java:495) ~[spigot-1.18.2-R0.1-SNAPSHOT.jar:3498-Spigot-b081915-10ba1be]
at dansplugins.dansessentials.Commands.BackCommand.execute(BackCommand.java:31) ~[?:?]
at preponderous.ponder.minecraft.bukkit.services.CommandService.interpretAndExecuteCommand(CommandService.java:55) ~[?:?]
at dansplugins.dansessentials.DansEssentials.onCommand(DansEssentials.java:73) ~[?:?]
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:45) ~[spigot-api-1.18.2-R0.1-SNAPSHOT.jar:?]
... 21 more