fix(abc:st): corrected error null value syntax

[cipchk]

• close st export column render没有导出/0 值导出为空 ng-alain#2463

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ng-alain/delon/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?

[x] Bugfix
[ ] Feature
[ ] 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
[ ] No

Other information

[ng-alain-bot]

Preview is ready!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7e61fc2) 94.94% compared to head (3367bed) 94.94%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1744   +/-   ##
=======================================
  Coverage   94.94%   94.94%           
=======================================
  Files         316      316           
  Lines        8908     8908           
  Branches     1767     1767           
=======================================
  Hits         8458     8458           
  Misses        379      379           
  Partials       71       71           

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[cipchk]

Preview is ready!