KnnVectorQueryBuilder does not respect allowUnmappedFields

[Mikep86]

Elasticsearch Version

8.13

Installed Plugins

No response

Java Version

bundled

OS Version

N/A

Problem Description

KnnVectorQueryBuilder does not respect the index.query.parse.allow_unmapped_fields index setting. If this is set to true (the default value), queries should be rewritten to MatchNoDocsQuery if the field specified in the query does not exist. However, KnnVectorQueryBuilder always returns an error in this case.

Steps to Reproduce

1. Create an index with default settings

PUT test-index 

2. Run a knn query against a missing field

GET test-index/_search
{
    "query": {
        "knn": {
            "field": "missing",
            "query_vector": [ 1.0, 2.0 ]
        }
    }
}

Logs (if relevant)

No response

[elasticsearchmachine]

Pinging @elastic/es-search (Team:Search)