Since I was the one who posted this, I feel that I should post the solution. Here is the group field I'm working with. This is used for the approval (or review) of a document. 

A Form is filled out and I use Workflow to fill in the values when the form hits the repository. My users also can add a reviewer later. When they do, I have instructed them to fill in the reviewer decision and the decision date. That does not always happen. So I build this piece into the daily workflow that runs on these documents and notifies the users that they need to review the document. 

The first thing I do is retrieve all 3 values from the group field. Then use a For Each Value on the reviewer decision multivalue token. if someone left this blank, there will be a null value, and the condition is looking for that. When it's found, I modify a token I use as an indicator. The next condition is looking at that indicator to see if it is on. When it is, I count the number of reviewers and the number of reviewer decisions. Then another For Each Value on the reviewers. I create an empty multi-value token for the 3 values in my group. I set the condition to compare the number of decisions to the iteration of the for Each Value. That way the first values that are valid are filled into the New token. Once that's done, the other branch runs on the remaining iterations and fills in the Reviewer name and my default values I want. The last step is to replace the values on the document with my new values. 

This process seems like more work than needed to accomplish the goal of ensuring there are no blanks in a group field and the only reason I need there to be no blanks is that the SDK script I use to update a value crashes when there are blanks. If there was a native activity to update group fields that wouldn't crash if there was a blank, then I wouldn't need this enhancement to my workflow to correct the blank.