use NULL instead of 0

bn_mp_set_double.c

@@ -37,7 +37,7 @@ int mp_set_double(mp_int *a, double b)
       return res;
    }
 
-   res = exp < 0 ? mp_div_2d(a, -exp, a, 0) : mp_mul_2d(a, exp, a);
+   res = exp < 0 ? mp_div_2d(a, -exp, a, NULL) : mp_mul_2d(a, exp, a);
    if (((cast.bits >> 63) != 0ULL) && (mp_iszero(a) == MP_NO)) {
       SIGN(a) = MP_NEG;
    }