Fix S3 event parsing when eventName is present but eventTime is not

[reifiedbeans]

Motivation and Context

Currently, S3EventNotification::fromJson throws an exception when eventTime is null. This is problematic, since the code intends to allow for this field to be null, but it uses the wrong variable when performing a guard.

Modifications

This patch fixes the null guard by using the correct variable, eventTime, before attempting to parse it as an Instant.

Testing

Built the project locally (couldn't build some modules locally, so I just built the one modified)

./mvnw --projects :s3-event-notifications --also-make install

Screenshots (if appropriate)

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING document
• Local run of mvn install succeeds
• My code follows the code style of this project
• My change requires a change to the Javadoc documentation
• I have updated the Javadoc documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed
• I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
• My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

• I confirm that this pull request can be released under the Apache 2 license