[SVLS-3853] handle empty function case in tag-object

[joeyzhao2018]

What does this PR do?

Fixes #464 (again, 😭 )

Motivation

Testing Guidelines

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)

[codecov-commenter]

Codecov Report

Attention: 117 lines in your changes are missing coverage. Please review.

Comparison is base (35295b3) 80.35% compared to head (d57c29f) 82.12%.
Report is 99 commits behind head on main.

❗ Current head d57c29f differs from pull request most recent head 626f525. Consider uploading reports for the commit 626f525 to get more accurate results

Files	Patch %	Lines
src/trace/listener.ts	53.84%	17 Missing and 1 partial ⚠️
src/trace/span-context-wrapper.ts	57.57%	13 Missing and 1 partial ⚠️
src/trace/span-inferrer.ts	83.33%	0 Missing and 10 partials ⚠️
src/trace/xray-service.ts	91.50%	8 Missing and 1 partial ⚠️
src/trace/step-function-service.ts	92.13%	6 Missing and 1 partial ⚠️
src/trace/cold-start-tracer.ts	87.23%	2 Missing and 4 partials ⚠️
src/utils/event-type-guards.ts	14.28%	6 Missing ⚠️
src/trace/context/extractor.ts	91.07%	5 Missing ⚠️
src/trace/context/extractors/sqs.ts	66.66%	4 Missing and 1 partial ⚠️
src/index.ts	91.66%	3 Missing and 1 partial ⚠️
... and 13 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #467      +/-   ##
==========================================
+ Coverage   80.35%   82.12%   +1.77%     
==========================================
  Files          36       54      +18     
  Lines        1761     2188     +427     
  Branches      410      510     +100     
==========================================
+ Hits         1415     1797     +382     
- Misses        294      329      +35     
- Partials       52       62      +10     

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