/**
 * Type guard that narrows a `SchemaObject` to the variant whose `type` is
 * `'null'`.
 *
 * The `'null'` type was introduced in OpenAPI 3.1 (aligning with JSON Schema
 * 2020-12). In OpenAPI 3.0, nullability is expressed via `nullable: true`,
 * not via `type: 'null'`.
 *
 * Works with `SchemaObject` types from OpenAPI 3.1 and 3.2.
 */
export declare const isNullSchema: <T>(schema: T) => schema is [Extract<T, {
    type: "null";
}>] extends [never] ? T & {
    type: "null";
} : Extract<T, {
    type: "null";
}>;
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