Nullability

Constraints are required by default. Two markers control optionality.

Nullable

Nullable() — marker that allows None. Required inside Each(...) since Each evaluates its constraints functionally.

NotNull

NotNull(*, message=None, code=None) — marker that forbids None and lets you customize the missing-value error message or code.

For top-level fields, prefer the standard T | None syntax — iron-monk natively intercepts Union and bypasses validation for missing data. Full discussion in Core Concepts → Nullability.