export declare const isUndefined: (obj: any) => obj is undefined; export declare const isObject: (fn: any) => fn is object; export declare const isPlainObject: (fn: any) => fn is object; export declare const validatePath: (path?: string) => string; export declare const isFunction: (fn: any) => boolean; export declare const isString: (fn: any) => fn is string; export declare const isConstructor: (fn: any) => boolean; export declare const isNil: (obj: any) => obj is null; export declare const isEmpty: (array: any) => boolean; export declare const isSymbol: (fn: any) => fn is symbol;