Hello, I don't know if its a bug or I'm doing something wrong calling the ThemeBuilder.
I extracted the Neptune theme skeleton and I'm changing it as I need. The problem happens when I call the themer.bat: it generates a .jar with blank icons in the menu folder, though other icons are fine.
For now I'm copying the original icons to the new .jar theme manually.

Generated checked.png: checked.png
Original checked.png: checked.png