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。

youdao

Reference types - same as pointer types, except that a reference type cannot be NULL.

引用类型—与指针类型相同，只是引用类型不能为NULL。

youdao

A null reference pointer was passed to the stub.

向占位程序传送了空的索引指针。

youdao