SOLR-17209: Fix NullPointerException in QueryComponent

[pvcnt]

https://issues.apache.org/jira/browse/SOLR-17209

Description

In our production deployment of Solr, running 8.6, we see the following stacktrace (truncated):

java.lang.NullPointerException at org.apache.solr.handler.component.QueryComponent.mergeIds(QueryComponent.java:873) at org.apache.solr.handler.component.QueryComponent.handleRegularResponses(QueryComponent.java:628) at org.apache.solr.handler.component.QueryComponent.handleResponses(QueryComponent.java:607)

Solution

Add a null check.

Tests

None.

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide

[epugh]

I'm hoping someone else with more experience can weigh in.... However, isn't the bug here that you can have a SolrServerException that doesn't have a cause? Shouldn't we just make sure we always have a cause? I'd love to see a unit test demonstrating where this happens normally, and therefore why the extra check is needed?

[pvcnt]

I have observed it in production (running on 8.6, granted). SolrServerException sure has a constructor that takes no cause, and is used at several places in Http2SolrClient, HttpSolrClient and LBSolrClient. I guess the extra check does not hurt, since the code definitely allows the cause to be null?

[dsmiley]

Eric: Exceptions are chained; the end of the chain has no cause. Any code that throws SSE directly (not due to some other exception) will result in this.

I know it's annoying but can you add a CHANGES.txt item and file a JIRA please?

[pvcnt]

@dsmiley I thought I could do the economy of it for such a small change. I created the issue and entry in CHANGES.txt.

[epugh]

@dsmiley do you want to shepherd this one? If not, I will, just let me know ;-). And thanks for explaining about the exceptions!

[dsmiley]

It'd be wonderful for you to; thanks Eric. Separately, I'm trying to combat the need for JIRAs; I hated asking for one here. Stay tuned.