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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-8.5@e2696ed). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #60440   +/-   ##
================================================
  Coverage               ?   57.0002%           
================================================
  Files                  ?       1769           
  Lines                  ?     628274           
  Branches               ?          0           
================================================
  Hits                   ?     358118           
  Misses                 ?     246109           
  Partials               ?      24047           

Flag	Coverage Δ
integration	36.9964% <0.0000%> (?)
unit	72.6847% <100.0000%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.8711% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.3064% <0.0000%> (?)

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[fixdb]

+1

[0xPoe]

Thanks!

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fixdb, Rustin170506

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• OWNERS [Rustin170506,fixdb]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-04-10 20:56:52.385392542 +0000 UTC m=+2376306.069628647: ☑️ agreed by fixdb.
• 2025-04-11 00:53:58.75690459 +0000 UTC m=+2390532.441140686: ☑️ agreed by Rustin170506.

[fixdb]

/retest