Fix array_index_out_of_bounds_exception when indexing documents with field name containing only dot

[gaobinlong]

Description

"." as field name yields array_index_out_of_bounds_exception, the reason is that we split the field name by . here:

OpenSearch/server/src/main/java/org/opensearch/index/mapper/DocumentParser.java

Line 208 in 49b7cd4

String[] parts = fullFieldPath.split("\\.");

,
, if the field name contains only dot, the split result is an empty array, then yields that exception in this line:

OpenSearch/server/src/main/java/org/opensearch/index/mapper/DocumentParser.java

Line 1045 in 0cde7ba

return objectMapper.getMapper(subfields[subfields.length - 1]);

.

Since . is reserved for object resolution, we can fail the indexing request when the field name contains only dot.

Related Issues

Resolves #14911

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 94c912e: 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 778f159: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.73%. Comparing base (49b7cd4) to head (2e4fdf5).
Report is 12 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #15126      +/-   ##
============================================
- Coverage     71.84%   71.73%   -0.11%     
+ Complexity    62820    62701     -119     
============================================
  Files          5169     5169              
  Lines        294664   294666       +2     
  Branches      42615    42616       +1     
============================================
- Hits         211691   211386     -305     
- Misses        65530    65820     +290     
- Partials      17443    17460      +17     

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[github-actions]

✅ Gradle check result for 2e4fdf5: SUCCESS

[gaobinlong]

@reta, mind taking a second look at this PR? Thank you!

[reta]

Thanks a lot, @gaobinlong !