### Added
- [`list.index_of`](https://aiken-lang.github.io/stdlib/aiken/list.html#index_of): For getting a values index in a list.
- [`transaction.placeholder`](https://aiken-lang.github.io/stdlib/aiken/transaction.html#placeholder): For constructing test transactions.
- [`transaction.value.is_zero`](https://aiken-lang.github.io/stdlib/aiken/transaction/value.html#is_zero): For checking whether a value is null.
### Changed
- [`value.to_minted_value`](https://aiken-lang.github.io/stdlib/aiken/transaction/value.html#to_minted_value) now correctly preserves the invariant of `MintedValue`: it always contain a null quantity of Ada.
### Removed
N/A