OBJ Export doesn't create mtl file

[Anonymous]

Hi,
I recently moved to AC23 from AC21, and I'm trying to reprogram my add-on accordingly. In the previous version, i used the ACAPI_CommndCall to export OBJ files automatically. I rewrote the code in my new Addon, and it does create the OBJ file, but without a material file (.mtl) next to it. If i save obj manually, the . mtl file is created properly.

Hoe can i make my add-on export OBJ files with MTL files, as it used to?

Thanks a lot!
Ido