Yeah - that’s a good approach. Getting the model to first move on the spline at all, and then fixing up any spacing issues sounds like a good process.
This error means the code is trying to read a value that is currently set to “None.” If you look at the Details panel of the Joe_Fixx actor, you’ll see there’s a new variable there for
Spline and SplineComp.
Open the dropdown for Spline, and select one of your spline objects in the scene. That will let the dragon know which spline you want it to follow.
(FYI: You don’t have to set SplineComp manually - this is the bit of code that does that, where it plucks the Spline component off the spline actor, so it can read in the information it needs)