Old school comment... back in the day, there were computers on which dereferencing the null pointer would in fact return zero. And given that a typical linked list is terminated by a null, mistakes could creep in where "points to a 0" was checked when "pointer is 0" should have been. Needless to say, code like this would crash in mysterious ways when compiled on a machine where location 0, while readable, had nonzero contents. The alternative, getting a segfault because 0 wasn't mapped, is preferable because then you see the problem right away.

Anyhow it's just barely possible that this assignment was a hack to make this sort of code work on a machine where address 0 is (uninitialized) nonzero and can be harmlessly made zero.