WORLDEDIT-2793 - Reported by robbzkupper

java.lang.NullPointerException
at java.util.Collections$UnmodifiableMap.(Unknown Source)
at java.util.Collections.unmodifiableMap(Unknown Source)
at com.sk89q.jnbt.CompoundTag.(CompoundTag.java:63)
at com.sk89q.worldedit.blocks.MobSpawnerBlock.getNbtData(MobSpawnerBlock.java:150)
at com.sk89q.worldedit.schematic.MCEditSchematicFormat.save(MCEditSchematicFormat.java:256)

While the row numbes don't match, I'm convinced it's caused by this line:

values.put("SpawnData", new CompoundTag("SpawnData", spawnData == null ? null : spawnData.getValue()));

This can call the CompundTag constructor with null, and the constructor forwards the null without further check to:

Collections.unmodifiableMap(value);

which then throws the NPE.

Possible fix would be to change the CompundTag constructor from:

public CompoundTag(String name, Map<String, Tag> value) {
    super(name);
    this.value = Collections.unmodifiableMap(value);
}

to:

public CompoundTag(String name, Map<String, Tag> value) {
    super(name);
    this.value = value != null ? Collections.unmodifiableMap(value) : Collections.EMPTY_MAP;
}

Comment by wizjany

How are you even getting this error? WE shouldn't use MobSpawnerBlock...

Comment by robbzkupper

Well, it does.

public void saveRegion(CuboidRegion region, File file) throws IOException, DataException {
	final Vector min = region.getMinimumPoint(), max = region.getMaximumPoint();
	try (OutputStream os = new FileOutputStream(file)) {
		EntityMCEditSchematicFormat.save(region.getWorld(), os, max.subtract(min).add(new Vector(1, 1, 1)), min, min);
	}
}

Comment by wizjany

that's not worldedit?

Comment by -.-

That's for plugin, using Worldedit.

Comment by wizjany

what plugin is this?

Comment by -.-

It's our private plugin. Exports worldguard regions, regeneretes world, pastes saved regions to old coordinates.