Fixed StringIndexOutOfBoundsException caused by empty index expressions

[nibix]

Description

This fixes a regression introduced by #18523 ; calling IndexNameExpressionResolver.concreteIndices() with an index expression containing an empty string should throw an IndexNotFoundException. However, this regressed to throwing a StringIndexOutOfBoundsException. This change fixes the issue.

Check List

• Functionality includes testing.

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[nibix]

Regarding a changelog entry:

This fixes an issue caused by a change that has not been released yet. Is for this a change log entry still wanted/necessary?

[github-actions]

❌ Gradle check result for c5d4c57: 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?

[cwperks]

Regarding a changelog entry:

This fixes an issue caused by a change that has not been released yet. Is for this a change log entry still wanted/necessary?

I added the skip-changelog label.

[github-actions]

❌ Gradle check result for c5d4c57: 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 c5d4c57: 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 c5d4c57: SUCCESS

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.12%. Comparing base (cb9c30b) to head (c5d4c57).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #19766      +/-   ##
============================================
- Coverage     73.12%   73.12%   -0.01%     
+ Complexity    70973    70963      -10     
============================================
  Files          5737     5737              
  Lines        324767   324768       +1     
  Branches      46982    46982              
============================================
- Hits         237483   237478       -5     
- Misses        68151    68163      +12     
+ Partials      19133    19127       -6     

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