[Cosmos] Fix ClassCastException when building CosmosException from an empty error response body

[marcellustavares]

Description

JsonSerializable.fromJson(String, ObjectMapper) performs an unchecked cast of the parsed tree to ObjectNode:

return (ObjectNode) objectMapper.readTree(json);

When json is empty or blank, ObjectMapper.readTree(...) returns a MissingNode (not an ObjectNode), so the cast throws ClassCastException: class ...MissingNode cannot be cast to class ...ObjectNode.

fixes #49322

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[github-actions]

Thank you for your contribution @marcellustavares! We will review the pull request and get back to you soon.

[marcellustavares]

@microsoft-github-policy-service agree company="Elastic"

[kushagraThapar]

This is blindly creating an empty ObjectNode when the jsonNode is not an instance of ObjectNode. That's not the right fix and is too broad for things like arrays returned, etc. Although agreed its already a bug in the SDK code, however, fix should take that into account (like ArrayNode types, etc.).

[kushagraThapar]

Thanks @marcellustavares for your contribution. Really appreciate it. We are discussing the correct fix for this internally, will post my findings here soon, thanks!