fix: revert Nullable

Author: antfu

src/array.ts

@@ -3,7 +3,7 @@ import { Arrayable, Nullable } from './types'
 /**
  * Convert Arrayable<T> to Array<T>
  */
-export function toArray<T>(array: Nullable<Arrayable<T>>): Array<T> {
+export function toArray<T>(array?: Nullable<Arrayable<T>>): Array<T> {
   array = array || []
   if (Array.isArray(array))
     return array
@@ -13,7 +13,7 @@ export function toArray<T>(array: Nullable<Arrayable<T>>): Array<T> {
 /**
  * Convert Arrayable<T> to Array<T>
  */
-export function flattenArrayable<T>(array: Nullable<Arrayable<T | Array<T>>>): Array<T> {
+export function flattenArrayable<T>(array?: Nullable<Arrayable<T | Array<T>>>): Array<T> {
   return toArray(array).flat(1) as Array<T>
 }
 

src/types.ts

@@ -3,20 +3,10 @@
  */
 export type Awaitable<T> = T | PromiseLike<T>
 
-/**
- * Null or underfind whatever
- */
-export type Nilable<T> = T | null | undefined
-
 /**
  * Null or whatever
  */
-export type Nullable<T> = T | null
-
-/**
- * Undefined or whatever
- */
-export type Undefineable<T> = T | undefined
+export type Nullable<T> = T | null | undefined
 
 /**
  * Array, or not yet