Fatal error: Default value for parameters with a class type hint can only be NULL in routes.php on line 472

I keep getting this error when I go to my forum after install. Install seemed to go well. However, when I try and open the forum this is what I get.

When I try and go to ADMIN, this is what I get:

Fatal error: Uncaught --> Smarty: unable to write file cache/smarty/templates_c/wrt5e4ed1499ec065_60632464 <-- thrown in sys/Ext/Smarty/sysplugins/smarty_internal_runtime_writefile.php on line 59

PHP Version 5.5.38
Mysql Version 5.6.43
Apache Server