CoreTermSearchFacetResult.terms() returns null if field is absent from all documents

Suggested Release Note:

Accessing the terms of a `TermFacet` result no longer throws NullPointerException if the target field is absent from all documents.

In Java, this surfaces as a NullPointerException when calling `TermSearchFacetResult.terms()`, as in this reproducer:

SearchResult result = cluster.searchQuery(

  "global_vector_index_5b698e",

  SearchQuery.matchAll(),

  SearchOptions.searchOptions()

    .facets(mapOf("facetName", TermFacet.term("absent-field", 3)))

);

TermSearchFacetResult facetResult = (TermSearchFacetResult)

        result.facets().get("facetName");

System.out.println(facetResult.terms()); // <--- NPE here

It's worse in Kotlin, where the results are converted eagerly; Kotlin gets an NPE inside `searchQuery`, before the user even touches the facet results.