playground: fix panic

[nexustar]

What problem does this PR solve?

• close panic: runtime error: invalid memory address or nil pointer dereference #2067

What is changed and how it works?

Check List

Tests

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

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release notes:

NONE

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• srstack

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[codecov-commenter]

Codecov Report

Base: 56.59% // Head: 56.60% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (109fbf3) compared to base (63d509b).
Patch coverage: 72.73% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2076      +/-   ##
==========================================
+ Coverage   56.59%   56.60%   +0.01%     
==========================================
  Files         313      313              
  Lines       33178    33178              
==========================================
+ Hits        18775    18778       +3     
+ Misses      12170    12168       -2     
+ Partials     2233     2232       -1     

Flag	Coverage Δ
playground	15.23% <72.73%> (+0.02%)	⬆️
tiup	16.47% <ø> (ø)
unittest	22.79% <0.00%> (ø)

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

Impacted Files	Coverage Δ
components/playground/playground.go	50.99% <72.73%> (+0.33%)	⬆️

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[nexustar]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 109fbf3