[OscarMasse]

Fixes #141.

Problem

With exactOptionalPropertyTypes: true in the consumer's tsconfig, every optional or nullable field fails the SchemaTypes constraint:

TS2375: Type 'OptionalModifier<VineString>' is not assignable to type 'SchemaTypes' with 'exactOptionalPropertyTypes: true'.

ConstructableSchema and ConstructableLiteralSchema declare isOptional?: boolean and allowNull?: boolean, while the modifiers forward their parent's value through getters typed boolean | undefined (for example get allowNull() { return this.#parent.allowNull }).
Under the flag, ?: boolean no longer accepts a present-but-undefined value, so the modifiers stop satisfying the interface they implement, and Infer<typeof schema> degrades to { [x: string]: any }.
This is the diagnosis @TomBeckett posted on the issue.

Fix

Widen both properties to boolean | undefined in the two interfaces, which is what the getters actually return.
Types only, no runtime change, and nothing changes for projects without the flag.

Verification

• npm run typecheck, lint and the test suite pass as before.
• A real application's validators (a few dozen vine.compile(vine.object(...)) schemas with optional and nullable fields), compiled with exactOptionalPropertyTypes: true and skipLibCheck: true: 116 errors against 4.4.0 (111 on allowNull, 5 on isOptional), 0 with this change.

[OscarMasse]

Hi! Friendly ping on this one. The CI workflows are waiting for maintainer approval (first-time contributor), so nothing has run yet. The change is types-only and still merges cleanly on 4.x after #158. Happy to adjust anything. Thanks!