fix: null type of values schema

[loomts]

resolve apecloud/kubeblocks#9381 in 09

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 42.80%. Comparing base (1533d82) to head (2832083).
Report is 21 commits behind head on release-0.9.

Files with missing lines	Patch %	Lines
pkg/util/flags/flags.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           release-0.9     #606      +/-   ##
===============================================
+ Coverage        42.79%   42.80%   +0.01%     
===============================================
  Files              183      183              
  Lines            26073    26071       -2     
===============================================
+ Hits             11157    11160       +3     
+ Misses           13597    13591       -6     
- Partials          1319     1320       +1     

Flag	Coverage Δ
unittests	42.80% <0.00%> (+0.01%)	⬆️

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