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

[ti-chi-bot]

@hawkingrei This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-7.5@1f0d8ff). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #59378   +/-   ##
================================================
  Coverage               ?   72.5389%           
================================================
  Files                  ?       1417           
  Lines                  ?     416932           
  Branches               ?          0           
================================================
  Hits                   ?     302438           
  Misses                 ?      94503           
  Partials               ?      19991           

Flag	Coverage Δ
unit	72.5389% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9400% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.5575% <0.0000%> (?)

[winoros]

/unhold

[0xPoe]

Thanks!

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [Rustin170506,winoros]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-02-21 08:01:57.884484601 +0000 UTC m=+1207560.280706663: ☑️ agreed by winoros.
• 2025-02-25 09:21:02.410535912 +0000 UTC m=+347610.363694178: ☑️ agreed by Rustin170506.

[0xPoe]

/retest