[Koha] Problem migrating 3.2 to 3.6

[Muhammad Abdullah]

Hello,

I'm attempting to upgrade from Koha version 3.2 to version 3.6 by just
copying over 3.2 db into a new instance of Koha 3.6. The webinstaller ran
just fine in bringing the db up to date, bar some errors about duplicate
fields that are already in the tables. However, I received these errors
when I ran "remove_items_from_biblioitems.pl" script, which produces the
following output:

"......................................................
Use of uninitialized value $biblioitem_tag in numeric ne (!=) at
/home/koha/kohaclone/C4/Biblio.pm line 3184.
Use of uninitialized value $biblio_tag in numeric ne (!=) at
/home/koha/kohaclone/C4/Biblio.pm line 3184.
Use of uninitialized value $biblio_subfield in string at
/home/koha/kohaclone/C4/Biblio.pm line 3216.
Use of uninitialized value $biblioitem_subfield in string at
/home/koha/kohaclone/C4/Biblio.pm line 3216.
Tag "" is not a valid tag. at /home/koha/kohaclone/C4/Biblio.pm line 3216"

Any help on how to solve this problem so that I can proceed with the
upgrade is very appreciated.