fawe undo error

[18:25:59] [Server thread/INFO]: FatherWh0 issued server command: //undo
[18:25:59] [Craft Scheduler Thread - 572/ERROR]: [WorldEdit] An unexpected error while handling a WorldEdit command
java.lang.reflect.InvocationTargetException
	at sun.reflect.GeneratedMethodAccessor107.invoke(Unknown Source) ~[?:?]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_51]
	at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_51]
	at com.sk89q.worldedit.util.command.parametric.ParametricCallable.call(ParametricCallable.java:243) ~[worldedit-bukkit-6.1.2.jar:?]
	at com.sk89q.worldedit.util.command.SimpleDispatcher.call(SimpleDispatcher.java:125) ~[worldedit-bukkit-6.1.2.jar:?]
	at com.sk89q.worldedit.extension.platform.CommandManager$1.run(CommandManager.java:253) [FastAsyncWorldEdit-bukkit19.jar:?]
	at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftTask.run(CraftTask.java:58) [patched_1.9.2.jar:git-Paper-727]
	at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53) [patched_1.9.2.jar:git-Paper-727]
	at com.destroystokyo.paper.ServerSchedulerReportingWrapper.run(ServerSchedulerReportingWrapper.java:22) [patched_1.9.2.jar:git-Paper-727]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.8.0_51]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.8.0_51]
	at java.lang.Thread.run(Unknown Source) [?:1.8.0_51]
Caused by: java.lang.NullPointerException
	at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:213) ~[patched_1.9.2.jar:git-Paper-727]
	at com.sk89q.worldedit.function.operation.ChangeSetExecutor.<init>(ChangeSetExecutor.java:51) ~[?:?]
	at com.sk89q.worldedit.function.operation.ChangeSetExecutor.createUndo(ChangeSetExecutor.java:94) ~[?:?]
	at com.sk89q.worldedit.EditSession.undo(EditSession.java:872) ~[?:?]
	at com.sk89q.worldedit.LocalSession.undo(LocalSession.java:265) ~[?:?]
	at com.sk89q.worldedit.command.HistoryCommands.undo(HistoryCommands.java:61) ~[?:?]
	... 12 more