SQL 2012 :: Rolling Up Multiple Row And Columns Into A Single Cell NULL Error

So I have a problem with combining cells: some of the cells are blank and some of the cells have NULL value.

The combined blank cells return perfect.

But the combined cells in which 1 or more contains NULL will return as NULL

0-4139-00-01OPTIONAL EQUIPMENT 139 - A -
0-4139-00-02NVG EQUIPMENT 139 - A -
0-4139-00-03NVG EQUIPMENT 139 - A -
0139-01-01BRAKE RESERVOIR NULL

A part of the script which i use is:

STUFF((SELECT ', ' + i.ac_type + ' - '
+ i.range_or_single+ ' ' + ' - ' + i.serialno_to
FROM msc_item_effectivity i
inner JOINmsc_item h
ONb.taskcard_verno_i = h.taskcard_verno_i
WHERE h.itemno_i = i.itemno_i
FOR XML PATH('')), 1, 1, '')

i.ac_type = 139
i.range_or_single = A
i.serialno_to = blank or NULL

I want the result of the blank value to be the same as the NULL value.

0139-01-01BRAKE RESERVOIR 139 - A -