Ojbect Reference error in intialization after upgrading to Epi 11

After upgrading to Episerver 11 from an earlier version you get an "Object reference not set to an instance of an object" error in the initialization step or you get a "ReadConfig()" error during the database migration.

This is caused by a breaking change in Episerver 11.0.0 where some objects where moved from the base EPiServer.Framework module to the EPiServer.Framework.aspnet module. To fix this go into your web.config file and look for:

<add virtualPath="~/cms/" physicalPath="modules\_protected" name="ProtectedAddons" type="EPiServer.Web.Hosting.VirtualPathNonUnifiedProvider, EPiServer.Framework"/>

And update it to read:

<add virtualPath="~/cms/" physicalPath="modules\_protected" name="ProtectedAddons" type="EPiServer.Web.Hosting.VirtualPathNonUnifiedProvider, EPiServer.Framework.aspnet"/>