There is an ongoing outage on the primary CPAN mirror. It is possible to work around the issue by using MetaCPAN as a mirror.

sub cache { my ($class, $value, $node) = @_; if ($node) { Class::RDF::Cache->cache->add( "_node:$value", $node ); return $node; } else { return Class::RDF::Cache->cache->get( "_node:$value" ); } }