ES|QL COMPLETION operator throws NPE

[benwtrent]

Elasticsearch Version

main

Installed Plugins

No response

Java Version

bundled

OS Version

any

Problem Description

It is possible for the completion operator to throw an NPE. I am not 100% sure the exact circumstances, but the logs don't lie.

Steps to Reproduce

N/A

Logs (if relevant)

java.lang.NullPointerException
	at java.util.Objects.requireNonNull(Objects.java:220)
	at java.util.ImmutableCollections$List12.<init>(ImmutableCollections.java:565)
	at java.util.List.of(List.java:935)
	at org.elasticsearch.xpack.esql.inference.completion.CompletionOperatorRequestIterator.inferenceRequest(CompletionOperatorRequestIterator.java:61)
	at org.elasticsearch.xpack.esql.inference.completion.CompletionOperatorRequestIterator.next(CompletionOperatorRequestIterator.java:54)

[elasticsearchmachine]

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

[elasticsearchmachine]

Pinging @elastic/search-eng (Team:SearchOrg)

[elasticsearchmachine]

Pinging @elastic/search-relevance (Team:Search - Relevance)

[afoucret]

@benwtrent Thank you for raising it. I reproduced the bug in a test and fixed it in #129235