Change maybe to use optional.

[codecov-commenter]

Codecov Report

Base: 64.25% // Head: 64.19% // Decreases project coverage by -0.05% :warning:

Coverage data is based on head (db6d131) compared to base (c54d8ac). Patch coverage: 64.28% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #87 +/- ## ========================================== - Coverage 64.25% 64.19% -0.06% ========================================== Files 4 4 Lines 1505 1486 -19 Branches 537 540 +3 ========================================== - Hits 967 954 -13 + Misses 47 41 -6 Partials 491 491 ``` | [Impacted Files](https://codecov.io/gh/BowenFu/hspp/pull/87?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bowen+Fu) | Coverage Δ | | |---|---|---| | [include/monadTrans.h](https://codecov.io/gh/BowenFu/hspp/pull/87/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bowen+Fu#diff-aW5jbHVkZS9tb25hZFRyYW5zLmg=) | `100.00% <ø> (ø)` | | | [include/hspp.h](https://codecov.io/gh/BowenFu/hspp/pull/87/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bowen+Fu#diff-aW5jbHVkZS9oc3BwLmg=) | `76.08% <64.28%> (+0.16%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bowen+Fu). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Bowen+Fu)

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