apply_filters( "add_{$meta_type}_metadata", null|bool $check, int $object_id, string $meta_key, mixed $meta_value, bool $unique )

80	 * @param null|bool $check      Whether to allow adding metadata for the given type.81	 * @param int       $object_id  ID of the object metadata is for.82	 * @param string    $meta_key   Metadata key.83	 * @param mixed     $meta_value Metadata value. Must be serializable if non-scalar.84	 * @param bool      $unique     Whether the specified meta key should be unique for the object.85	 */86	$check = apply_filters( "add_{$meta_type}_metadata", null, $object_id, $meta_key, $meta_value, $unique );87	if ( null !== $check ) {88		return $check;89	}90 91	if ( $unique && $wpdb->get_var(92		$wpdb->prepare(