Since a NULL pointer terminates a list, we can also use the NULL pointer condition as a base case for many of our recursive functions on linked lists.

由于 NULL 指针会结束一个链表，所以我们也可以使用 NULL 指针条件作为基于链表的很多递归程序的基线条件。

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That means a reference type can have a null pointer, but a value type cannot have a null value.

这意味着引用类型可能有空指针，但是数值类型不能有空值。

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Unfortunately, many designers have still not learnt that the special null pointer or null object is an equally bad idea.

遗憾的是，许多设计者并没有认识到空指针或空对象带来的危害。

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