Object Reference exception on running Add-SPSiteSubscriptionProfileConfig

In case you see an "Object reference" exception on running Add-SPSiteSubscriptionProfileConfig to configure UPA in a multi-tenant mode, there is a possibility that that the user context against which Add-SPSiteSubscriptionProfileConfig is run does not have access over UPA Service Application. Make sure you give the account access on Profile Service Application by clicking on "Permissions" in the ribbon and grant access to the current user account running the PS script.