fixListBug

[xinyual]

Description

Fix list bug when pass empty list

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.34%. Comparing base (2b76e3c) to head (103fccf).
Report is 55 commits behind head on main.

Files with missing lines	Patch %	Lines
.../main/java/org/opensearch/agent/tools/PPLTool.java	50.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #541      +/-   ##
============================================
+ Coverage     81.78%   82.34%   +0.55%     
- Complexity      193      356     +163     
============================================
  Files            11       17       +6     
  Lines           961     1688     +727     
  Branches        137      241     +104     
============================================
+ Hits            786     1390     +604     
- Misses          121      203      +82     
- Partials         54       95      +41     

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[Hailong-am]

better to have a unit test