Bug 37316: Treat empty string barcodes as undef

To test:
1.Add the following to MarcItemFieldsToOrder:

homebranch: 949$a
holdingbranch: 949$b
itype: 949$y
nonpublic_note: 949$x
public_note: 949$z
loc: 949$c
ccode: 949$8
notforloan: 949$7
uri: 949$u
copyno: 949$t
price: 949$g|949$j
replacementprice: 949$v
itemcallnumber: 949$o
quantity: 949$k
budget_code: 949$l
coded_location_qualifier: 949$f
enumchron: 949$h

2. Add the following to MarcFieldsToOrder:

price: 949$g
quantity: 949$k
budget_code: 949$l
discount: 949$m
sort1: 949$n
sort2: 949$q

3. Acquisitions > Find a vendor
4. Create a new basket -> Add to basket -> From new file
5. Use the file uplodaded in this bug report.
6. Set format to MARCXML and stage for import.
7. Add staged files to basket
8. Select all, make sure you add an item type, and choose 'Do not look for matching records'
9. Save and kaboom.
10. APPLY PATCH and restart_all
11. Follow the steps again, this time no kaboom.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit b68373ae42)
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

Koha/Item.pm

@@ -98,6 +98,9 @@ sub store {
         $self->itype($self->biblio->biblioitem->itemtype);
     }
 
+    # Ensure barcode is either defined or undef
+    $self->barcode(undef) if $self->barcode eq '';
+
     $self->barcode( C4::Circulation::barcodedecode( $self->barcode ) );
 
     my $today  = dt_from_string;