Fatal error: Uncaught TypeError:

The plugin sounds like just what I need to limit crawling by bad bots. Unfortunately when I try to activate it there seems to be a bug. Pretty sure I have uploaded the files properly and everything, and anyway, this TypeError seems like a code bug.

Wp version is still 4.9.11 (not liking the Gutenberg editor), PHP is 7.

( ! ) Fatal error: Uncaught TypeError: Return value of Shieldon\Shieldon::setSessionId() must be an instance of Shieldon\void, none returned in /opt/lampstack-7.0.23-0/apache2/htdocs/wp-content/plugins/wp-shieldon/vendor/terrylinooo/shieldon/src/Shieldon/Shieldon.php on line 655
( ! ) TypeError: Return value of Shieldon\Shieldon::setSessionId() must be an instance of Shieldon\void, none returned in /opt/lampstack-7.0.23-0/apache2/htdocs/wp-content/plugins/wp-shieldon/vendor/terrylinooo/shieldon/src/Shieldon/Shieldon.php on line 655
Call Stack
#	Time	Memory	Function	Location
1	0.0001	370624	{main}( )	.../plugins.php:0
2	0.4697	8966248	plugin_sandbox_scrape( )	.../plugins.php:172
3	0.4697	8966664	include( '/opt/lampstack-7.0.23-0/apache2/htdocs/wp-content/plugins/wp-shieldon/wp-shieldon.php' )	.../plugin.php:1897
4	0.4706	9052744	wpso_instance( )	.../wp-shieldon.php:181
5	0.4706	9054216	WPSO_Shieldon_Guardian->__construct( )	.../wpso-helper-functions.php:268
6	0.4707	9061008	Shieldon\Shieldon->__construct( )	.../class-wpso-shieldon.php:38
7	0.4707	9061008	Shieldon\Shieldon->setSessionId( )	.../Shieldon.php:244