message: Add OptStr test case to LOWER & UPPER tests
diff: use crate::*;
  test_case!(upper_lower, async move {
  - use Value::Str;
  + use Value::{OptStr, Str};
  let test_cases = vec![
  - ("CREATE TABLE Item (name TEXT)", Ok(Payload::Create)),
  (
  - r#"INSERT INTO Item VALUES ("abcd"), ("Abcd"), ("ABCD")"#,
  + "CREATE TABLE Item (name TEXT, opt_name TEXT NULL)",
  + Ok(Payload::Create),
  + ),
  + (
  + r#"INSERT INTO Item VALUES ("abcd", "efgi"), ("Abcd", NULL), ("ABCD", "EfGi")"#,
  Ok(Payload::Insert(3)),
  ),
  (
  @@ -41,6 +44,16 @@ test_case!(upper_lower, async move {
  "abcd".to_owned() "ABCD".to_owned()
  )),
  ),
  + (
  + "SELECT LOWER(opt_name), UPPER(opt_name) FROM Item;",
  + Ok(select!(
  + "LOWER(opt_name)" | "UPPER(opt_name)"
  + OptStr | OptStr;
  + Some("efgi".to_owned()) Some("EFGI".to_owned());
  + None None;
  + Some("efgi".to_owned()) Some("EFGI".to_owned())
  + )),
  + ),
  (
  "SELECT LOWER() FROM Item",
  Err(EvaluateError::NumberOfFunctionParamsNotMatching {
  