I just had a case where a batch MARC import script (not part of Koha, but maintained separately) had put some records with an empty 942 field into the database. The MARCXML looked something like this:

  <datafield tag="887" ind1=" " ind2=" ">
    <subfield code="a">x</subfield>
  </datafield>
  <datafield tag="942" ind1=" " ind2=" ">
  </datafield>
  <datafield tag="950" ind1=" " ind2="k">
    <subfield code="a">y</subfield>
  </datafield>


When trying to view these records, the following message was displayed:

The record you requested does not exist

But all the data were in the biblio, biblioitems, biblio_metadata tables. It was not possible to view the the record in the editor either. 

Would it be possible to catch this error and say something like "The record you requested has fatal errors" instead of telling the user it does not exist? 

Relevant code in catalogue/detail.pl:

 78 my $record       = GetMarcBiblio({ biblionumber => $biblionumber });
 79 my $biblio = Koha::Biblios->find( $biblionumber );
 80 $template->param( 'biblio', $biblio );
 81 
 82 if ( not defined $record ) {
 83     # biblionumber invalid -> report and exit
 84     $template->param( unknownbiblionumber => 1,
 85                       biblionumber => $biblionumber );
 86     output_html_with_http_headers $query, $cookie, $template->output;
 87     exit;
 88 }

This reports unknownbiblionumber => 1 when $record is not defined, but it does not differentiate between "biblionumber does not exist" and "biblionumber points to a broken MARCXML record".