fix: avoid nil pointer dereference

[okaybase]

Please answer these questions before submitting a pull request, or your PR will get closed.

Why submit this pull request?

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What changes will this PR take into?

Please update this section with detailed description.

Related issues

fix/resolve:
avoid nil pointer dereference

Checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

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[codecov-commenter]

Codecov Report

Merging #2061 (09ea60a) into master (e8503a0) will decrease coverage by 13.17%.
The diff coverage is 100.00%.

❗ Current head 09ea60a differs from pull request most recent head d8521df. Consider uploading reports for the commit d8521df to get more accurate results

@@             Coverage Diff             @@
##           master    #2061       +/-   ##
===========================================
- Coverage   66.11%   52.94%   -13.18%     
===========================================
  Files         121       38       -83     
  Lines        3226     2935      -291     
  Branches      787        0      -787     
===========================================
- Hits         2133     1554      -579     
- Misses       1093     1188       +95     
- Partials        0      193      +193     

Flag	Coverage Δ
backend-unit-test	52.94% <100.00%> (?)
frontend-e2e-test	?

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

Impacted Files	Coverage Δ
api/internal/handler/data_loader/route_export.go	71.23% <100.00%> (ø)
...mponents/Upstream/components/active-check/Type.tsx
...ream/components/active-check/Healthy/Successes.tsx
web/src/components/Plugin/UI/limit-count.tsx
web/src/components/PluginFlow/constants.ts
web/src/pages/SSL/Create.tsx
...omponents/passive-check/Unhealthy/HttpStatuses.tsx
...b/src/components/Plugin/UI/referer-restriction.tsx
web/src/components/Upstream/components/Scheme.tsx
web/src/pages/User/Login.tsx
... and 150 more

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