fix: Let event fields be nullable

[iamareebjamal]

Fixes #7252

[houndci-bot]

Black would make changes.

[codecov]

Codecov Report

Merging #7251 into development will increase coverage by 0.52%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development    #7251      +/-   ##
===============================================
+ Coverage        63.02%   63.55%   +0.52%     
===============================================
  Files              259      259              
  Lines            13034    13034              
===============================================
+ Hits              8215     8284      +69     
+ Misses            4819     4750      -69     

Impacted Files	Coverage Δ
app/api/events.py	37.50% <ø> (+14.50%)	⬆️
app/api/schema/events.py	96.89% <ø> (+5.29%)	⬆️
app/api/schema/settings.py	100.00% <0.00%> (ø)
app/models/setting.py	94.01% <0.00%> (+0.05%)	⬆️
app/api/helpers/permission_manager.py	58.88% <0.00%> (+0.34%)	⬆️
app/models/user.py	61.79% <0.00%> (+1.12%)	⬆️

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