Visitor Group membership issue after upgrading to CMS 12

Description

Fixed errors that occurred when you tried to add and save visitor group membership criterion after you upgraded to Optimizely Content Management System (CMS 12), (suspected to be related to an upgrade of the EPiServer.Find.Cms package from version 14.2.4 to 15.2.0). Additionally, unified search functionality was compromised so that only pages without visitor group configurations appeared in search results (unless the user was an administrator).

Steps to reproduce:

1. Upgrade CMS to version 12 and EPiServer.Find.Cms package to version 15.2.0.
2. Create a visitor group that has another visitor group as a member.
3. Attempt to add a new membership criterion to this nested visitor group and save.
4. Perform a unified search for pages. Only pages without visitor group configurations appear, (unless logged in as an administrator).