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Is null

isNull validates that a value is exactly null.

It performs a strict null check and rejects any value that is not null. If the value is not null, the rule emits a single validation event. Otherwise, it produces no validation output.

Signature

Through the API:

.isNull()

And internally:

export const isNull: ValidationRule
(value: unknown, path: FieldPath) => Promise<ReadonlyArray<JaneEvent>>

Events

Event code Description
value.not.null Value is not exactly null

Design rationale

  • Provides a strict, predictable null value validation.
  • Accepts only the exact null value.
  • Rejects undefined, empty strings, and other falsy values.
  • Never coerces or normalizes — validation is explicit and opt-in.
  • Emits exactly one event per failure for clarity and composability.
  • Async-compatible and returns a readonly array of JaneEvent objects.

Invoke

isNull runs only when explicitly included in a boundary or pipeline. It does not run automatically.

The rule activates when:

  • The value is any JavaScript value.
  • If the value is not exactly null, emits value.not.null.
  • If the value is null → returns an empty result set.

Examples

Valid null value

await isNull(null, "$");
// → []

Undefined value

await isNull(undefined, "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "value.not.null",
//       path: "$",
//       ...
//     }
//   ]

Other values

await isNull("", "$");
// → [
//     JaneEvent{
//       kind: "error",
//       code: "value.not.null",
//       path: "$",
//       ...
//     }
//   ]