# declare lexical variable *outside the scope of the eval*
my $BusUrl;

# trap potential error
eval {
  $BusUrl = $contact->getElementsByTagName( "BusinessUrl" );
};
# check if tag retrieval failed
if($@) {
  # assign an empty (but defined) string
  $BusUrl = '';
}

$bus_url = $BusUrl->item( 0 )->getChildAtIndex( 0 )->getData();