private String toString(Type type) {
        return switch (type) {
            case NIX -> "null";
            case BOOL -> "boolean";
            case LONG -> "integer";
            case DOUBLE -> "float";
            case STRING, DATA -> "string";
            case ARRAY -> "array";
            case OBJECT -> "object";
        };
    }
@return true if the JSON field was present but its value was 'null'
vespajlib/src/main/java/ai/vespa/json/Json.java