- improved parameter check

bin/slubsipbuilderbagit.pl

@@ -222,7 +222,7 @@ package SLUB::LZA::SIPBuilderBagIt;
     }
 
     sub add_marc21_schema_location($) {
-        if(! defined $_[0]) { croak "marc xml document required!"; }
+        if(ref($_[0]) ne 'XML::LibXML::Document') { croak "marc xml document required!"; }
         my $marc_doc = $_[0];
         my $root = $marc_doc->findnodes('/*[local-name()="record"]')->[0]; # get root element (XML::LibXML::Element)
         $root->setAttribute('xmlns:xsi', 'http://www.w3.org/2001/XMLSchema-instance'); # add xsi namespace (simple)