[GOBBLIN-1820] Add null default value to observability events that are additionally …

[Will-Lo]

…added

Dear Gobblin maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• My PR addresses the following Gobblin JIRA issues and references them in the PR title. For example, "[GOBBLIN-XXX] My Gobblin PR"
  • https://issues.apache.org/jira/browse/GOBBLIN-1820

Description

• Here are some details about my PR, including screenshots (if applicable):
  Additional fields to GaaSObservabilityEventExperimental should default to null so that kafka producers can properly register the schema.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

• My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

[codecov-commenter]

Codecov Report

Merging #3682 (8c3d96d) into master (9640ef0) will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #3682      +/-   ##
============================================
+ Coverage     46.85%   46.86%   +0.01%     
- Complexity    10754    10759       +5     
============================================
  Files          2138     2138              
  Lines         84021    84021              
  Branches       9337     9337              
============================================
+ Hits          39365    39374       +9     
+ Misses        41060    41053       -7     
+ Partials       3596     3594       -2     

see 5 files with indirect coverage changes

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[phet]

sorry not to have caught this before. I know that the default value must be first in the union type... but still that it must be explicitly named for use as the default.... didn't notice it was missing previously