fix: handle additional undefined series

[ryugaraj]

Description

A very niche case of point being null causing charts to crash in CloudWatch Console.

Only manage to reproduce in CloudWatch.

Optional chaining the access to series to handle null/undefined cases.

How has this been tested?

Tested in CloudWatch Console.

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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