Caused by 5c79f2d0fb
.
If no valid node_start is provided, we can just skip (e.g.
'ntree_shader_bump_branches' is not done then, but this is not
neccessary without a valid eevee output node anyways...).
Maniphest Tasks: T70441
Reviewed By: fclem
Differential Revision: https://developer.blender.org/D5969