When retrieving a record via the OAI-PMH interface, if one of the fields used
to prepare the DC metadata is not defined in the MARC framework (e.g.,
biblioitems.publicationyear in the default MARC21 framework), an OAI GetRecord
can fail with the following error:
> Can't call method "as_string" on an undefined value at
> /usr/share/koha/opac/cgi-bin/opac/oai.pl line 59.
Signed-off-by: Galen Charlton <galen.charlton@liblime.com>
