add type guard for isNotNil

[xiaoxiangmoe]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[x] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

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[codecov]

Codecov Report

Merging #4431 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4431      +/-   ##
==========================================
+ Coverage   92.23%   92.24%   +<.01%     
==========================================
  Files         522      522              
  Lines       11104    11104              
  Branches     2016     2016              
==========================================
+ Hits        10242    10243       +1     
  Misses        435      435              
+ Partials      427      426       -1

Impacted Files	Coverage Δ
components/core/util/check.ts	85.29% <ø> (ø)	⬆️
components/time-picker/time-holder.ts	96.49% <0%> (+0.87%)	⬆️

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[simplejason]

Sorry for this PR, we need to roll back this PR because it does not meet our commit specification.