fix null exception in text docs data set

[ylwu-amzn]

Description

[Describe what this change achieves]

Issues Resolved

[List any issues this PR will resolve]

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

Merging #1403 (4f5b0a4) into main (358354c) will decrease coverage by 1.24%.
Report is 7 commits behind head on main.
The diff coverage is 57.98%.

@@             Coverage Diff              @@
##               main    #1403      +/-   ##
============================================
- Coverage     78.82%   77.58%   -1.24%     
- Complexity     2145     2180      +35     
============================================
  Files           168      173       +5     
  Lines          8755     8977     +222     
  Branches        878      889      +11     
============================================
+ Hits           6901     6965      +64     
- Misses         1455     1608     +153     
- Partials        399      404       +5     

Flag	Coverage Δ
ml-commons	77.58% <57.98%> (-1.24%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...rg/opensearch/ml/client/MachineLearningClient.java	100.00% <100.00%> (ø)
...earch/ml/engine/algorithms/TextEmbeddingModel.java	100.00% <100.00%> (ø)
...thms/sparse_encoding/SparseEncodingTranslator.java	100.00% <100.00%> (ø)
...rse_encoding/TextEmbeddingSparseEncodingModel.java	100.00% <100.00%> (ø)
...ing/HuggingfaceTextEmbeddingServingTranslator.java	100.00% <ø> (ø)
...NNXSentenceTransformerTextEmbeddingTranslator.java	67.04% <ø> (ø)
...ng/SentenceTransformerTextEmbeddingTranslator.java	100.00% <100.00%> (+2.38%)	⬆️
...rithms/text_embedding/TextEmbeddingDenseModel.java	91.30% <100.00%> (ø)
...va/org/opensearch/ml/engine/utils/ScriptUtils.java	90.00% <100.00%> (+13.52%)	⬆️
...tion/prediction/TransportPredictionTaskAction.java	78.26% <100.00%> (+0.48%)	⬆️
... and 10 more