I'm getting an error... unsure why

[Sjmarf]

I am using a Mac. The program runs, but returns this error:

An error has occurred while converting the world!
java.util.NoSuchElementException: Structures
at br.com.gamemods.nbtmanipulator.NbtCompound.require(nbt.kt:452)
at br.com.gamemods.nbtmanipulator.NbtCompound.getCompound(nbt.kt:534)
at br.com.gamemods.j2nwc.internal.JavaChunk.(JavaChunk.kt:97)
at br.com.gamemods.j2nwc.internal.Chunk_converterKt.toNukkit(chunk-converter.kt:13)
at br.com.gamemods.j2nwc.internal.RegionFileConverter.toNukkit(RegionFileConverter.kt:39)
at br.com.gamemods.j2nwc.internal.RegionFileConverter.convertRegionFile(RegionFileConverter.kt:19)
at br.com.gamemods.j2nwc.WorldConverter.convert(WorldConverter.kt:105)
at br.com.gamemods.j2nwc.WorldConverterCLI.main(WorldConverterCLI.kt:83)
The world conversion has failed

Any idea how I could fix this? Thanks!