[BottomNav] Dynamically generating tabs when the BottomNav has a class applied crashes #7611

Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 6.0.0
• Cross-platform modules: 6.0.2
• Android Runtime: 6.0.0
• iOS Runtime: 6.0.0
• Plugin(s):

Describe the bug
If you dynamically generate tabs when the BottomNavigation control has a class applied to it, the applications crashes.

To Reproduce
https://play.nativescript.org/?template=play-tsc&id=GDzvl9&v=2
Tap on Change button

Expected behavior
To work 😀

Related to #6967.