Can't merge chunks

[xplorer]

Hello !

Please, i'm a bit new to this "chunks" technic.

i attempted to do a small test with three chunks which overlap a bit, and each with a dense cloud calculated.
I'd like to merge them but it's either generating a merged chunk without dense cloud Inside, or later , not even generating a merged chunk, and telling me "Null color data !" , i don't understand what it means.

Please, What am i doing wrong ?

Thanks !