I enabled the required item 122 (dragon egg) to fly to stations.

RequiredItem:
Item: 122
For:
toStation: true

Then when I enter /dt travel without having the egg on me, I get the in-game message:

An internal error occured while attempting to perform this command

[08:41:43] [Server thread/INFO]: tschaffter issued server command: /dt travel test
[08:41:43] [Server thread/ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'dt' in plugin DragonTravel vPhoenix v0.0.1.5
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at org.bukkit.craftbukkit.v1_8_R2.CraftServer.dispatchCommand(CraftServer.java:646) ~[spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at net.minecraft.server.v1_8_R2.PlayerConnection.handleCommand(PlayerConnection.java:1133) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at net.minecraft.server.v1_8_R2.PlayerConnection.a(PlayerConnection.java:968) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at net.minecraft.server.v1_8_R2.PacketPlayInChat.a(PacketPlayInChat.java:45) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at net.minecraft.server.v1_8_R2.PacketPlayInChat.a(PacketPlayInChat.java:1) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at net.minecraft.server.v1_8_R2.PlayerConnectionUtils$1.run(SourceFile:13) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_33]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_33]
at net.minecraft.server.v1_8_R2.SystemUtils.a(SourceFile:60) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at net.minecraft.server.v1_8_R2.MinecraftServer.A(MinecraftServer.java:710) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at net.minecraft.server.v1_8_R2.DedicatedServer.A(DedicatedServer.java:368) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at net.minecraft.server.v1_8_R2.MinecraftServer.z(MinecraftServer.java:651) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at net.minecraft.server.v1_8_R2.MinecraftServer.run(MinecraftServer.java:554) [spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_33]
Caused by: java.lang.IllegalArgumentException: Material cannot be null
at org.apache.commons.lang.Validate.notNull(Validate.java:192) ~[spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at org.bukkit.craftbukkit.v1_8_R2.inventory.CraftInventory.contains(CraftInventory.java:92) ~[spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
at eu.phiwa.dt.movement.Travels.toStation(Travels.java:258) ~[?:?]
at eu.phiwa.dt.commands.CommandHandler.onCommand(CommandHandler.java:451) ~[?:?]
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot-1.8.3.jar:git-Spigot-26dfd01-ad2f806]
... 15 more

The same error occurs when I have the dragon egg in my inventory.

i have exacly the same problem, but also with payment by items

Which version of DragonTravel do you run?

.15 here
im esmic on the bukkit forums also. posting in this thread http://dev.bukkit.org/bukkit-plugins/dragontravel/tickets/230-failure-to-use-required-items-and-payment-by-items/

here is screenshot from today

@tschaffter Totally forgot about this issue. Fixed it in commit fc2a7ac, will be included in next release.

Thanks! 👍