planner: Fix load stats failure when stats file contains with null (#57818)

[ti-chi-bot]

This is an automated cherry-pick of #57818

What problem does this PR solve?

Issue Number: close #53966

Problem Summary:
Fix load stats failure when stats file contains with null

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[fixdb]

+1

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-6.5@5e39597). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-6.5     #59173   +/-   ##
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  Misses                 ?      76401           
  Partials               ?      16721           

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fixdb, winoros

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• OWNERS [winoros]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-02-05 09:00:32.514561429 +0000 UTC m=+262304.046973422: ☑️ agreed by fixdb.
• 2025-02-17 06:40:32.516354888 +0000 UTC m=+857074.912576949: ☑️ agreed by winoros.