Bugfix/619 faculty page rendering fails on null absences

[Urjikoo]

Types of changes

• [X] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [X] I have run eslint on the code
• [ ] I have added JSDoc for all of my code (where applicable)
• [ ] I have added tests to cover my changes.

Priority:

• [X] Normal
• [ ] High

Related Issues:

Fixes #619

[Urjikoo]

This PR addresses the issue where faculty page fails to render when faculty member is added without an absence data. The issue was when absence is null, it fails to update the absence type and fails to render but it now it should render empty space and that resolves rendering issue.

[codecov[bot]]

Codecov Report

Merging #626 (300b645) into develop (a0f7aa5) will decrease coverage by 0.02%. The diff coverage is 16.66%.

@@             Coverage Diff             @@
##           develop     #626      +/-   ##
===========================================
- Coverage    95.24%   95.21%   -0.03%     
===========================================
  Files          192      192              
  Lines         4475     4553      +78     
  Branches       541      555      +14     
===========================================
+ Hits          4262     4335      +73     
- Misses         100      102       +2     
- Partials       113      116       +3     

Impacted Files	Coverage Δ
src/client/components/layout/AppHeader.tsx	92.00% <ø> (ø)
src/client/components/layout/AppRouter.tsx	82.60% <0.00%> (ø)
...rc/client/components/pages/Faculty/FacultyPage.tsx	92.39% <0.00%> (-2.06%)	:arrow_down:
.../components/pages/Faculty/FacultyScheduleTable.tsx	100.00% <ø> (ø)
src/client/components/pages/FacultyAdmin.tsx	100.00% <ø> (ø)
.../client/components/pages/Schedule/ScheduleView.tsx	94.87% <ø> (ø)
.../client/components/pages/utils/absenceToVariant.ts	81.81% <0.00%> (-18.19%)	:arrow_down:
src/common/constants/absenceType.ts	100.00% <100.00%> (ø)
...rc/server/courseInstance/courseInstance.service.ts	95.34% <0.00%> (-1.53%)	:arrow_down:
src/server/course/course.service.ts	100.00% <0.00%> (ø)
... and 3 more

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