Fix potential NPE for switch statement when null case is missing

[gaobinlong]

Description

In previous some PRs that replace explicit type conversion with instanceof pattern variable: #19979 and #19938, we change some if...else to switch...case, one issue is that if null case is missing in switch, once the switch value is null, NPE will be thrown, so this PR aims to fix the potential NPE for the preivous change.

Related Issues

No issue.

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 0df3ac1: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 0df3ac1: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for 0df3ac1: SUCCESS

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.36%. Comparing base (acdae04) to head (1293555).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
...g/opensearch/common/inject/internal/MoreTypes.java	82.35%	2 Missing and 1 partial ⚠️
.../java/org/opensearch/painless/ir/ConstantNode.java	0.00%	1 Missing ⚠️
.../org/opensearch/common/inject/internal/Errors.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #20044      +/-   ##
============================================
+ Coverage     73.27%   73.36%   +0.09%     
- Complexity    71541    71641     +100     
============================================
  Files          5789     5789              
  Lines        327153   327160       +7     
  Branches      47157    47154       -3     
============================================
+ Hits         239729   240032     +303     
+ Misses        68185    67903     -282     
+ Partials      19239    19225      -14     

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[github-actions]

✅ Gradle check result for ff22894: SUCCESS

[github-actions]

❌ Gradle check result for 1293555: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for 1293555: SUCCESS

[sandeshkr419]

LGTM, thanks for adding the test cases for the changes as well!