Net::OAI::ListRecords - Results of the ListRecords OAI-PMH verb.
You probably don't want to be using this method yourself, since Net::OAI::Harvester::listRecords() calls it for you.
Return the next metadata object or undef if there are no more.
Returns the name of the package being used to represent the individual metadata records. If unspecified it defaults to Net::OAI::Record::OAI_DC which should be ok.