Skinned Mesh Renderer - Root Bone returns as null

Not sure if this is the right place for this or if it should be somewhere else.
I made and rigged a model in Blender and brought it over into Unity. I’m trying to make it into an UMA race, but I’m running into a problem with the imported model’s skinned mesh renderer. In the editor I can see the Root Bone field is filled with the transform of my armature’s Root bone (this is obviously correct). But when UMA attempts to access it in code, renderer.rootBone is returning a null. I have no idea why this is or how to fix it.

i face the same problem