fix attribute error on null values in field serialization

[sainak]

Proposed Changes

• fix attribute error on null values in field serialization

Associated Issue

• fixes Unable to create consultation with declare death decision after consultation care_fe#8276
• fixes AttributeError: 'NoneType' object has no attribute '_meta' #2347

Merge Checklist

• Tests added/fixed
• Update docs in /docs
• Linting Complete
• Any other necessary step

Only PR's with test cases included and passing lint and test pipelines will be reviewed

@coronasafe/care-backend-maintainers @coronasafe/care-backend-admins

[sentry-io]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: care/facility/events/handler.py

Function	Unhandled Issue
create_consultation_events	AttributeError: 'NoneType' object has no attribute '_meta' /api/v1/con... Event Count: 2

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Project coverage is 63.70%. Comparing base (ee747c6) to head (1e955a5).

Files	Patch %	Lines
care/utils/event_utils.py	0.00%	13 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2348      +/-   ##
===========================================
- Coverage    63.71%   63.70%   -0.01%     
===========================================
  Files          238      238              
  Lines        13376    13378       +2     
  Branches      1906     1907       +1     
===========================================
  Hits          8522     8522              
- Misses        4504     4506       +2     
  Partials       350      350              

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[nihal467]

LGTM