prop_number_size return?

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

The manpage for prop_number_size says (identical in 9.1 and 5.2)

     prop_number_size(prop_number_t number)
            Returns 8, 16, 32, or 64, representing the number of bits required
            to hold the value of the object.  If the supplied object isn't a
            numeric value, NULL is returned.

This indicates severe type confusion, since NULL is for pointers, not
integers, and, indeed, the return type in the .h and the manpage is
int.  Should that be 0, or (int)NULL, or what?  C doesn't promise that
(int)NULL isn't, for example, 32 (though for all I know POSIX may);
while I doubt it would be anything but 0 on any NetBSD system, I am
uncomfortable with that sort of nonportability, even when using
something like -lprop.

For what it's worth, the implementation (again, both 9.1 and 5.2)
specifies 0, not NULL, in its return statement for the non-number case.

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