ES|QL "ROW a=null | SORT a" crashes with AssertionError

[jan-elastic]

Elasticsearch Version

9.0.0

Installed Plugins

No response

Java Version

n/a

OS Version

n/a

Problem Description

Executing the ES|QL command

ROW a=null | SORT a

crashes on main with the following assertion error:

[2025-02-03T15:33:10,801][ERROR][o.e.b.ElasticsearchUncaughtExceptionHandler] [runTask-0] fatal error in thread [elasticsearch[runTask-0][search][T#1]], exiting java.lang.AssertionError: estimated row size [0] wasn't set
	at org.elasticsearch.xpack.esql.planner.LocalExecutionPlanner.planTopN(LocalExecutionPlanner.java:362)
(...)

Note: this doesn't occur in production, because assertions are disabled.

Steps to Reproduce

spin up ES, Kibana, go to discover, ES|QL mode, enter "ROW a=null | SORT a"

Logs (if relevant)

No response

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)