Add note about NULL handling in BIT_COUNT function

[way0utwest]

Clarified behavior of BIT_COUNT with NULL values.

[prmerger-automator]

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[learn-build-service-prod]

Learn Build status updates of commit aa8de06:

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[v-regandowner]

@thesqlsith

Can you review the proposed changes?

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@MicrosoftDocs/public-repo-pr-review-team

[Copilot]

Pull request overview

Clarifies the documented behavior of BIT_COUNT when the input expression is NULL, ensuring readers understand the function’s null-propagation behavior.

Changes:

• Added a note stating that BIT_COUNT returns NULL when passed a NULL expression.

[learn-build-service-prod]

Learn Build status updates of commit 93195ff:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/t-sql/functions/bit-count-transact-sql.md	✅Succeeded

For more details, please refer to the build report.