fix(module: table): exception if field is null

[ElderJames]

[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• Site / documentation update
• Demo update
• Component style update
• Bundle size optimization
• Performance optimization
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

💡 Background and solution

📝 Changelog

Language	Changelog
🇺🇸 English
🇨🇳 Chinese

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• Changelog is provided or not needed

[codecov-io]

Codecov Report

Merging #965 (f134dc2) into master (7314300) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master    #965      +/-   ##
=========================================
- Coverage    5.76%   5.76%   -0.01%     
=========================================
  Files         406     406              
  Lines       21727   21731       +4     
=========================================
  Hits         1252    1252              
- Misses      20475   20479       +4     

Impacted Files	Coverage Δ
components/table/Column.razor	0.00% <0.00%> (ø)
components/table/ColumnContext.cs	0.00% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6de05f3...f134dc2. Read the comment docs.