Fix Generic ErrorProne/NullAway/JavaStyleGuide warnings

[ndegwamartin]

Description of what I changed

Fixes the generic ErrorProne/NullAway/JavaStyleGuide warnings

Resolves #1457

E2E test

TESTED:

Please replace this with a description of how you tested your PR beyond the
automated e2e/unit tests.

Checklist: I completed these to help reviewers :)

• I have read and will follow the
  review process.

• I am familiar with Google Style Guides for the language I have coded in.

  No? Please take some time and review
  Java and
  Python style guides.

• My IDE is configured to follow the Google
  code styles.

  No? Unsure? ->
  configure your IDE.

• I have added tests to cover my changes. (If you refactored existing
  code that was well tested you do not have to add tests)

• I ran mvn clean package right before creating this pull request and
  added all formatting changes to my commit.

• If I made any Python code changes, I ran black . and pylint . right
  before creating this pull request and added all formatting changes to my
  commit.

• All new and existing tests passed.

• My pull request is based on the latest changes of the master branch.

  No? Unsure? -> execute command git pull --rebase upstream master

[codecov-commenter]

Codecov Report

❌ Patch coverage is 53.57143% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.67%. Comparing base (a70dab1) to head (df14bdb).

Files with missing lines	Patch %	Lines
...ava/com/google/fhir/analytics/PipelineManager.java	0.00%	3 Missing ⚠️
.../com/google/fhir/analytics/AvroConversionUtil.java	0.00%	2 Missing ⚠️
.../java/com/google/fhir/analytics/FhirStoreUtil.java	0.00%	1 Missing and 1 partial ⚠️
...com/google/fhir/analytics/view/ViewApplicator.java	50.00%	0 Missing and 2 partials ⚠️
.../java/com/google/fhir/analytics/FetchPatients.java	0.00%	1 Missing ⚠️
...c/main/java/com/google/fhir/analytics/FhirEtl.java	0.00%	1 Missing ⚠️
...in/java/com/google/fhir/analytics/ResourceTag.java	0.00%	0 Missing and 1 partial ⚠️
...hir/analytics/metrics/PipelineMetricsEndpoint.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1488      +/-   ##
============================================
+ Coverage     46.66%   46.67%   +0.01%     
  Complexity      676      676              
============================================
  Files            90       90              
  Lines          5874     5868       -6     
  Branches        814      814              
============================================
- Hits           2741     2739       -2     
+ Misses         2828     2824       -4     
  Partials        305      305              

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