I had a layer being driven by Templater that had the same name as the comp it was in. So in my my case:
Comp name > DATE
Layer in that comp > DATE
To make it work, all I had to do was change the name of that comp to something different than the layer inside.
I guess Templator saw that comp as an empty layer, that’s why I was getting the “null is not an object” error.
It’s all a little over my head and I’m probably not explaining it correctly, but the people at Dataclay were very kind in helping me figure it out!