Calling a method or accessing a member of an undefined object will throw a fatal error that looks like this:  "can't call method * on an undefined value at ..."

For example, this code will cause a software error if $data->{itemnumber} exists, but the item doesn't exist (maybe it's been deleted?):

my $item = Koha::Items->find( $data->{itemnumber} );

my $biblio = $item->biblio;

How this is handled will of course depend on context -- maybe we should carp and continue, or maybe just

I would like to add a coding standard that we always check for this.

Thanks,

--Barton