Fix schedule null api URL

[DGoiana]

When a student does not have their schedule yet, the page does not have the required tag to access the api url.

Review checklist

• [ ] Terms and conditions reflect the current change
• [ ] Contains enough appropriate tests
• [ ] If aimed at production, writes a new summary in whatsnew/whatsnew-pt-PT
• [ ] Properly adds an entry in changelog.md with the change
• [ ] If PR includes UI updates/additions, its description has screenshots
• [ ] Behavior is as expected
• [ ] Clean, well-structured code

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 16%. Comparing base (8a518bc) to head (593a4cd). Report is 4 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1316 +/- ## ======================================= Coverage 16% 16% ======================================= Files 239 239 Lines 7172 7172 ======================================= Hits 1078 1078 Misses 6094 6094 ```