telendt opened a new pull request, #1051:
URL: https://github.com/apache/solr/pull/1051

   This commit removes unnecessary check for `omitNorms` from 
`FieldLengthFeatureScorer` that otherwise causes `NullPointerException` in 
`FieldLengthFeature` for non-stored or missing fields.
   
   https://issues.apache.org/jira/browse/SOLR-13219
   
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   # Description
   
   I recently encountered a problem with using `FieldLengthFeature` with 
non-stored fields where feature extraction/LTR reranking would result in 
`NullPointerException`. I check the `FieldLengthFeature` docs and briefly 
inspected implementation to check if for using this feature storing fields is 
really required. According to my expectations it's not required - the only 
required information are norms, that my field has enabled.
   
   I search Solr Jira and found 
[SOLR-13219](https://issues.apache.org/jira/browse/SOLR-13219) that seemed very 
similar in nature. Upon investigation I found that the two issues have indeed 
the same origin. The root cause seems to be the following line:
   
   ```java
   final IndexableField idxF = searcher.doc(0).getField(field);
   ```
   That returns null for non-stored missing fields.
   
   Honestly, I don't understand why `FieldLengthFeatureScorer `even checks 
whether the field omits norms or not. It's only used in 
`FieldLengthFeature#scorer` and this method already checks whether norms are 
there or not (and if they are missing a constant 0 ValueFeatureScorer is 
returned).
   
   # Solution
   
   I removed the problematic code.
   
   # Tests
   
   I modified `title` and `description` fields (`stored="false"`) in 
`schema.xml` proving that existing tests still work as long as the problematic 
code is removed (without it `TestFieldLength#testRanking` is failing). With 
this change I also had to slightly change 
`TestFeatureLogging#testGeneratedFeatures` test, but without changing its logic.
   
   I also added `TestFieldLength#testRankingDynamicField` test to prove that 
`TestFieldLength` works correctly with dynamic fields too, and doesn't fail if 
one (or more) documents from rerank candidate set lacks specific field.
   
   # Checklist
   
   Please review the following and check all that apply:
   
   - [x] I have reviewed the guidelines for [How to 
Contribute](https://wiki.apache.org/solr/HowToContribute) and my code conforms 
to the standards described there to the best of my ability.
   - [x] I have created a Jira issue and added the issue ID to my pull request 
title.
   - [x] I have given Solr maintainers 
[access](https://help.github.com/en/articles/allowing-changes-to-a-pull-request-branch-created-from-a-fork)
 to contribute to my PR branch. (optional but recommended)
   - [x] I have developed this patch against the `main` branch.
   - [x] I have run `./gradlew check`.
   - [x] I have added tests for my changes.
   - [ ] I have added documentation for the [Reference 
Guide](https://github.com/apache/solr/tree/main/solr/solr-ref-guide)
   


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