如果不存在，则容器提供一个事务。

If one does not exist, the container supplies one.

youdao

如果不存在，就把设置为并返回。

If doesn't exist, set to and return.

youdao

如果不存在或者是NULL，就返回。

If doesn't exist or is NULL, return.

youdao

On the other hand, if out of sight out of mind, they should expect the screen to keep going.

另一方面,如果看不见就觉得不存在,那么婴儿会期待屏板继续移动

耶鲁公开课 - 心理学导论课程节选

So if you don't actually assign to something, it falls on the floor and the value goes away.

所以是，如果你没有赋值，它掉在地上，那个值就不存在了。

哈佛公开课 - 计算机科学课程节选

To sort of give you a quick taste, if after my death I won't exist, how could anything be bad for me?

让你们先来体会一下，如果在我死后，我不存在了，对我来说怎么会有坏事情？

耶鲁公开课 - 死亡课程节选