function bbp_topic_subscriptions_metabox( $post ) {

	// Current user subscription
	$input_value = bbp_is_user_subscribed( bbp_get_current_user_id(), $post->ID )
		? 'bbp_subscribe' // maintain existing subscription
		: '';             // do not add or remove subscription

	// Get user IDs
	$user_ids = bbp_get_subscribers( $post->ID );

	// Output
	?>
	<input name="bbp_topic_subscription" id="bbp_topic_subscription" type="hidden" value="<?php echo esc_attr( $input_value ); ?>" />
	<p><?php

		// Relationships
		$args = array(
			'include' => $user_ids
		);

		// Users were found
		if ( ! empty( $user_ids ) && bbp_has_users( $args ) ) :
			bbp_metabox_user_links();

		// No users
		else :
			esc_html_e( 'No users have subscribed to this topic.', 'bbpress' );
		endif;

	?></p><?php

	do_action( 'bbp_subscriptions_metabox', $post );
}