How to add one section separator for Navigation Drawer in Android?

Question

I have a navigation drawer like this image. I want to add a section separator (like the line separating Neptune). It seems simple but I can\'t find anything on the web that

Answer 1

Make sure you define each group with a unique ID, separator won't appear without the ID.

For example, this is my drawer_menu.xml:

Gabriel adds below in the comments that if the group doesn't have an id, the separator will not appear.