什么时候否定 JSDoc 中的 return 值?

When does one negate the return value in JSDoc?

我在 Protractor 文档中看到了很多,

/**
 * ...
 * ...
 *
 * @returns {!webdriver.promise.Promise} A promise which resolves to the
 *     number of elements matching the locator.
 */

return 对象的 否定 是怎么回事?什么时候使用?

我承认也许它不是严格意义上的 "negation," 但符号应该记录在某处。

谢谢!

根据JSDoc spec

Non-nullable type

{!number} A number, but never null

Indicates that the value is of the specified type, but cannot be null.