SOLR-17381 SolrJ fix to fetch entire ClusterState if asked

[aparnasuresh85]

Description

Address a test failure in ClusterStateProviderTest.testGetClusterStatus when ClusterStateProvider (CSP) chosen is Http2ClusterStateProvider. More importantly, while ClusterStateProvider.getClusterStatus() is highly discouraged, it should still be functional since there are codepaths using it.

Solution

If a call to get CLUSTERSTATUS intending to get collections data specifies a null value for collection parameter, proceed to fetch entire cluster status since fetching the remaining (live_nodes, cluster properties, roles etc) should not be time consuming anyway.

Tests

Ensure ClusterStateProviderTest.testGetClusterState() passes when chosen CSP is Http2ClusterStateProvider. (Currently the test fails with a NPE)

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, not available for branches on forks living under an organisation)
• 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

[dsmiley]

minor: These params.set calls are passing "true" | "false" but there's a nice boolean (i.e. a "sugar" method) for the primitive. Could you change that please? It's a minor matter I know but you wrote this code not long ago.

I understand how this change fixes the bug but it feels like the solution optimizes for the smallest possible adequate fix. I look at the method's caller, fetchClusterState. By its name, it should be fetching the cluster's state, but it's kind of working in two modes -- everything or one collection. Can we have fetchClusterState do only the whole cluster (and pass null to submitClusterStateRequest for the request type to signify everything) and have a different/new fetchCollectionState method that only gets the state of one collection, returning a DocCollection? That will be the common code path, and this recommendation I propose would clarify what little work is pertinent to that code path. If this seems like too much, feel free to push back.

Also, I observe that the clusterProperties param is unused (always given null, I mean). Unsure if this is a recent bug/oversight.