On command:
/area save test -n testnamespace
/area save test

In game result:
An error has occurred. See console:

In console:
[17:22:25 INFO]: korho issued server command: /area save test [17:22:25 WARN]: com.sk89q.minecraft.util.commands.WrappedCommandException: java.lang.NullPointerException [17:22:25 WARN]: at com.sk89q.minecraft.util.commands.CommandsManager.invokeMethod(CommandsManager.java:534) [17:22:25 WARN]: at com.sk89q.minecraft.util.commands.CommandsManager.executeMethod(CommandsManager.java:514) [17:22:25 WARN]: at com.sk89q.minecraft.util.commands.CommandsManager.executeMethod(CommandsManager.java:469) [17:22:25 WARN]: at com.sk89q.minecraft.util.commands.CommandsManager.execute(CommandsManager.java:407) [17:22:25 WARN]: at com.sk89q.craftbook.bukkit.CraftBookPlugin.onCommand(CraftBookPlugin.java:768) [17:22:25 WARN]: at com.sk89q.bukkit.util.DynamicPluginCommand.execute(DynamicPluginCommand.java:55) [17:22:25 WARN]: at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:159) [17:22:25 WARN]: at org.bukkit.craftbukkit.v1_16_R3.CraftServer.dispatchCommand(CraftServer.java:810) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.PlayerConnection.handleCommand(PlayerConnection.java:2023) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.PlayerConnection.c(PlayerConnection.java:1838) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.PlayerConnection.a(PlayerConnection.java:1791) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.PacketPlayInChat.a(PacketPlayInChat.java:47) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.PacketPlayInChat.a(PacketPlayInChat.java:5) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.PlayerConnectionUtils.lambda$ensureMainThread$1(PlayerConnectionUtils.java:23) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.TickTask.run(SourceFile:18) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.IAsyncTaskHandler.executeTask(IAsyncTaskHandler.java:136) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.IAsyncTaskHandler.executeNext(IAsyncTaskHandler.java:109) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.MinecraftServer.bb(MinecraftServer.java:1138) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.MinecraftServer.executeNext(MinecraftServer.java:1131) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.IAsyncTaskHandler.awaitTasks(IAsyncTaskHandler.java:119) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.MinecraftServer.sleepForTick(MinecraftServer.java:1092) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.MinecraftServer.w(MinecraftServer.java:1006) [17:22:25 WARN]: at net.minecraft.server.v1_16_R3.MinecraftServer.lambda$a$0(MinecraftServer.java:175) [17:22:25 WARN]: at java.base/java.lang.Thread.run(Thread.java:834) [17:22:25 WARN]: Caused by: java.lang.NullPointerException [17:22:25 WARN]: at com.sk89q.craftbook.mechanics.area.AreaCommands.saveArea(AreaCommands.java:66) [17:22:25 WARN]: at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [17:22:25 WARN]: at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) [17:22:25 WARN]: at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [17:22:25 WARN]: at java.base/java.lang.reflect.Method.invoke(Method.java:566) [17:22:25 WARN]: at com.sk89q.minecraft.util.commands.CommandsManager.invokeMethod(CommandsManager.java:526) [17:22:25 WARN]: ... 24 more

WorldEdit version: 7.2.3+5680-135941e
CraftBook version: 3.10.3;4680-f1ee2df
AsyncWorldEdit version: 3.8.2
Full logfile as attachment.
ef2a7f.txt

Try without AWE, forks of worldedit (especially AWE) are known to break the WorldEdit API, and therefore plugins using it.

Cannot be reproduced, and comments weren't addressed. Closing unless further information is provided leading to reproduction.