Fix one panic error when sts processDelete

[TaoZou1]

Pass nil to processDelete to avoid panic

Test Done:
run ut

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 77.10%. Comparing base (3499a03) to head (f9fb282).

Files with missing lines	Patch %	Lines
.../controllers/statefulset/statefulset_controller.go	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1444      +/-   ##
==========================================
- Coverage   77.32%   77.10%   -0.22%     
==========================================
  Files         169      169              
  Lines       23325    23332       +7     
==========================================
- Hits        18036    17991      -45     
- Misses       3954     3955       +1     
- Partials     1335     1386      +51     

Flag	Coverage Δ
unit-tests	77.10% <87.50%> (-0.22%)	⬇️

Files with missing lines	Coverage Δ
.../controllers/statefulset/statefulset_controller.go	72.69% <87.50%> (-18.98%)	⬇️

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[TaoZou1]

e2e

[TaoZou1]

/e2e