Filters the site data before the get_sites query takes place.
Description
Return a non-null value to bypass WordPress' default site queries. The expected return type from this filter depends on the value passed in the request query vars: <ul> <li>When $this->query_vars['count'] is set, the filter should return the site count as an integer.</li> <li>When 'ids' === $this->query_vars['fields'], the filter should return an array of site IDs.</li> <li>Otherwise the filter should return an array of WP_Site objects.</li> </ul> Note that if the filter returns an array of site data, it will be assigned to the sites property of the current WP_Site_Query instance. Filtering functions that require pagination information are encouraged to set the found_sites and max_num_pages properties of the WP_Site_Query object, passed to the filter by reference. If WP_Site_Query does not perform a database query, it will not have enough information to generate these values itself.
Parameters
$site_data\WP_Site[]|int[]|int|null
Return an array of site data to short-circuit WP's site query, the site count as an integer if $this->query_vars['count'] is set, or null to run the normal queries.