Ran across a few more issues while fixing error handling issues. So I'll bundle those fixes into this ticket as well:
FacetStream: was throwing NPE with zero facet results. TODO: add a test case for this. This effects the SQLHandler operating in facet aggregationMode.
GatherNodesStream: explain was breaking on the admin stream console, due to issues with toExpression.
CloudSolrStream: was throwing NPE on missing params rather then throwing proper exception. TODO: add test case for this.
GraphHandler: did not have the SelectStream registered.
Overall though the changes made in
SOLR-8467 are looking good and the new admin stream console is working well.