[9.1] ESQL: Fix NPE on empty to_lower/to_upper call (#131917)#131924

elasticsearchmachine merged 2 commits intoelastic:9.1elastic/elasticsearch:9.1from

GalLalouche:backport/9.1/pr-131917GalLalouche/elasticsearch:backport/9.1/pr-131917Copy head branch name to clipboard