Lazy-loads term meta for queued terms.
This method is public so that it can be used as a filter callback. As a rule, there is no need to invoke it directly.
(mixed) (Required) The
$checkparam passed from the 'get_term_metadata' hook.
(mixed) In order not to short-circuit
get_metadata(). Generally, this is
null, but it could be another value if filtered by a plugin.