500 Internal Server Error when enabling birthday calendar or sharing without existing calendar

[he-hu]

Bug Description

When a new user is created and "Include birthday calendar" is set
to "Yes" before any calendar exists, a 500 Internal Server Error occurs.
Same issue when trying to activate sharing without an existing calendar.

Steps to reproduce

1. Create a new user
2. Immediately set "Include birthday calendar = Yes" → Save
3. → 500 Internal Server Error

Workaround

1. First create a calendar for the user
2. Then enable "Include birthday calendar" or sharing
   → Works correctly

Environment

• Davis version: latest (davis-standalone)
• Database: MariaDB 10.11
• Deployed via Docker