Finish location not working in flow

Question

So I have a flow so that users can create cases.

In my current flow Screen Input -> record create -> Thank you screen. I want users to go back from the thank you screen and edit what they wrote without creating duplicate records, So I changed the order of operations. It would be Screen Input -> thank you -> record create. The problem with this is that my Finish_location is not working. I get the following error:

The Visualforce page code:

<apex:page controller="Quick_Case" >
    <flow:interview name="Quick_Case" interview="{!flowInstance}" finishLocation="{!FinishLocation}" buttonLocation="bottom">
        <apex:param name="Role" value="{!$User.UserRoleId}"/>
        <apex:param name="Department" value="{!$User.Department}"/>
        <apex:param name="CurrUserID" value="{!$User.Id}"/>
    </flow:interview>
</apex:page>

The Apex Class:

public class Quick_Case {

    Public Flow.Interview.Quick_Case flowInstance{get; set;}

    Public PageReference getFinishLocation() {

        String ID = '';
        if(flowInstance != null)
            ID = flowInstance.caseid;

        PageReference send = new PageReference('/' + ID);
        send.setRedirect(true);
        return send;       
    }        
}

Answer 1

The thank you screen needs to be after the record create this causes the visualforce page to refresh and retrieve the newly generated record id. Initially it will load with a null id.