fix: empty strings should be treated as having no value when merge

[ybzky]

close https://github.com/dream-num/univer-pro/issues/3046

Pull Request Checklist

• Related tickets or issues have been linked in the PR description (or missing issue).
• Naming convention is followed (do please check it especially when you created new plugins, commands and resources).
• Unit tests have been added for the changes (if applicable).
• Breaking changes have been documented (or no breaking changes introduced in this PR).

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Playwright test results

 19 passed

Details

 19 tests across 9 suites
 4 minutes, 40 seconds
 81acccf
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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 32.71%. Comparing base (39d0d46) to head (81acccf).
Report is 12 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #3963      +/-   ##
==========================================
+ Coverage   32.46%   32.71%   +0.25%     
==========================================
  Files        2427     2438      +11     
  Lines      126046   126501     +455     
  Branches    28196    28333     +137     
==========================================
+ Hits        40915    41380     +465     
+ Misses      85131    85121      -10     

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