I realize this is an old question but I just figured out a way to accomplish what I needed with this so I thought I'd post what I found. In order to have null fields included, I added an evaluated expression attribute to the data model using this formula:
if(isnull(field),"Field is Null", field)
When I created the pivot from the data model and used the calculated attribute, I could SPLITROW on it and all data is included (since by the time SPLITROW saw the field, there were no null values).
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