import Constraints from './Constraints';
declare class Null extends Constraints {
    message?: string;
    isValid(value: any): boolean;
}
/**
 * 验证配置元素的值必须为 `null`或者`undefined`
 */
declare const _default: {
    (options: import("../../servlets/annotations/Target").CreateOptions<typeof Null>): (target: Object, name: string, p?: number) => any;
    (target: {
        [x: string]: any;
    }, propertyKey: string): any;
    (target: {
        [x: string]: any;
    }, propertyKey: string, parameterIndex: number): any;
} & import("../../servlets/annotations/annotation/type").LinkAnnotationType<typeof Null> & typeof Null;
export default _default;