Fix Jira webhook JSONException with null timetracking values - JENKINS-75783

[daviddiblasio]

Note: This is for archival/reference only — no action expected from maintainers. Leaving this here in case someone forks or takes over the project in the future. Maybe someone can find this approach useful.

Fixed Jira webhook JSONException by implementing recursive null value preprocessing. Jira changed from empty objects to explicit null values, causing parser failures. Created WebhookJsonPreprocessor that strips ALL null values while preserving valid data.

Root Cause: Jira changed webhook payload format from empty objects to explicit null values:

// Old format (working)
"timetracking": {}

// New format (causing JSONException)
"timetracking": {
  "originalEstimate": null,
  "remainingEstimate": null,
  "timeSpent": null,
  "originalEstimateSeconds": null,
  "remainingEstimateSeconds": null,
  "timeSpentSeconds": null
}

Fixes: JENKINS-75783 - JSONException when processing Jira webhook payloads with null timetracking values after Jira v10.3.7 upgrade.

Testing done

• WebhookJsonPreprocessorTest: Verifies recursive null removal from nested JSON structures, handling of mixed valid/null values, processing of comment arrays with null visibility fields, and preservation of valid data while removing null values
• WebhookNullTimetrackingIntegrationTest: Verifies end-to-end webhook processing with null timetracking values for both changelog and comment events
• All tests pass successfully: ./gradlew test --tests WebhookJsonPreprocessorTest and ./gradlew test --tests WebhookNullTimetrackingIntegrationTest
• Backward compatibility verified: existing webhook payloads continue to work correctly while new null-containing payloads are properly processed

Manual testing confirmed functionality with Jira webhook payloads containing null timetracking values, verifying both changelog and comment webhook events process without JSONException.

Submitter checklist

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