GIST_LEAF vs. leaf_key; gist?entryinit

In the examples I've seen, in the consistent method we have:

if (GIST_LEAF(entry)) [...]

but in compress we have:

if (entry->leafkey) [...]

I can see what the latter's doing, but I'm not sure what GIST_LEAF
does, or why you'd want to use it.

Also, I noticed this in src/backend/access/gist:

static void gistcentryinit(GISTSTATE *giststate, int nkey,
GISTENTRY *e, Datum k,
Relation r, Page pg,
OffsetNumber o, int b, bool l, bool isNull);

and later (in gistPageAddItem):

gistcentryinit(giststate, 0, &tmpcentry, dentry->key, r, page,
offsetNumber, dentry->bytes, FALSE);

Isn't the call missing the "isNull" parameter?

--
Itai Zukerman <http://www.math-hat.com/~zukerman/>