Beginner problem with global templates

Heyho,

I have a beginner question/problem regarding the correct use of global templates.
https://panel.holoviz.org/how_to/templates/template_set.html#global-template

I have copied the example code for a global template from the provided link and started panel with
python -m panel serve example.py --show

The application shows normally in my browser but also adds a red warning stating:
Application did not publish any contents

Ensure you have marked items as servable or added models to the bokeh document manually.

I have not changed the original code from the example on the holoviz page. This is the terminal output:
2024-08-15 07:00:31,754 Starting Bokeh server version 3.5.1 (running on Tornado 6.4.1)
2024-08-15 07:00:31,757 User authentication hooks NOT provided (default user enabled)
2024-08-15 07:00:31,764 Bokeh app running at: http://localhost:5006/test_panel
2024-08-15 07:00:31,764 Starting Bokeh server with process id: 21337
2024-08-15 07:00:33,691 WebSocket connection opened
2024-08-15 07:00:33,692 ServerConnection created

What is the issue?

Best regards,

Marcus

Have you added .servable() to any of your widgets?