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

[limwa]

Thank you ❤️

[codecov]

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

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

[rubuy-74]

LGTM 🚀