in_array(): Argument #2 ($haystack) must be of type array, null given in in_array()

Problem/Motivation

rocketship_core_link_alter causes a deprecation error for the in_array function on line 879 of rocketship_core.module when no classes where added to the variables array:
TypeError: in_array(): Argument #2 ($haystack) must be of type array, null given in in_array() (line 879 of /var/www/html/docroot/modules/contrib/rocketship_core/rocketship_core.module).