Bug 10388: Does not display 'null' after editing an item on receiving

Bug 10388: Does not display 'null' after editing an item on receiving

After editing an item on receiving, 'null' is displayed if no value is
defined for a field. It should be blank.

Test plan:
0/ Set AcqCreateItem to 'ordering'
1/ Go on the receipt page page
2/ Edit an item
3/ Does not fill all values
4/ Confirm that undefined values are replaced with an empty string

NOTE: I think you meant receive. Editing requires at least clicking
      the dropdown value, even if you don't change it before
      clicking save. null's appeared. Post patch application was
      able to get nulls to disappear. :)

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>