requireNil

function requireNil(
  value: unknown,
  message: string = "Expected null or undefined."
): null | undefined;

The absent values, and only those: 0, "" and false are present values and do not qualify.

isX and nonX answer a question and never interrupt control flow; requireX and requireNonX hand the value back or throw. The scheme is explained in Validation conventions.

Parameters

Parameter	Type	Description
`value`	`unknown`	The value to validate.
`message` (optional) `= "Expected null or undefined."`	`string`	The message of the exception. A default is used when omitted.

Returns

null | undefined — the same value, typed as null or undefined.

Throws

Exception	Condition
`IllegalArgumentException`	the value is not `null` or `undefined`.

Examples

What passes and what does not

requireNil(null); // => null
requireNil(undefined); // => undefined
requireNil(0); // throws IllegalArgumentException
requireNil(""); // throws IllegalArgumentException

Source

src/lang/base/requireNil.ts

23 September 2026

This documentation was generated with AI (Claude) from the library's source code.

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