Fix 4990, allow null values in S3 object metadata

[dropofwill]

Change tests to check keys in any order instead of relying on keySets implicit ordering.

Motivation and Context

Fixes #4990

Modifications

Collect with HashMap instead of built in Java collector which cannot handle nulls.

Testing

Added a test with null keys, fails without my change, passes with it.

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

[debora-ito]

@dropofwill I apologize for the slow turnaround. The issue was fixed in a different PR #5238.