Function coalesce

nodedb-query/src/expr_parse/parser.rs:536–540

()

    #[test]
    fn coalesce() {
        let (expr, _) = parse_ok("COALESCE(description, '')");
        let doc = Value::from(serde_json::json!({"description": null}));
        assert_eq!(expr.eval(&doc), Value::String("".into()));
    }

    #[test]
    fn case_when() {