Passing NULL to a function called with OidFunctionCall3

Hey all,

I'm trying to make use of OidFunctionCall3 and am wondering how to
resolve an issue.  I need to be able to pass to the function called with
OidFunctionCall3 a NULL and am having difficulty figuring out how.

{{{
/* build fcnarg */
for (i = 0; i < set_count; i++) {
    if (_haspixel[i]) {
        fcnarg[i] = Float8GetDatum(_pixel[i]);
        POSTGIS_RT_DEBUGF(4, "arg %d is %f", i, _pixel[i]);
    }
    else {
        fcnarg[i] = (Datum) NULL;
        POSTGIS_RT_DEBUGF(4, "arg %d is NULL", i);
    }
}
datum = OidFunctionCall3(fcnoid, fcnarg[0], fcnarg[1], fcnuserarg);
}}}

The above does not work (segfault).  What is the correct way to pass a
NULL to the function being called?  Should I be using a different
function other than OidFunctionCall3?

Thanks,
Bborie
--
Bborie Park
Programmer
Center for Vectorborne Diseases
UC Davis
530-752-8380
bkpark@ucdavis.edu