Clearing the Parent Bone field in relations would result in something like this: ``` add_relation(Bone Parent) - Could not find op_from (ComponentKey(OBArmature, BONE)) add_relation(Bone Parent) - Failed, but op_to (ComponentKey(OBEmpty, TRANSFORM)) was ok ERROR (bke.object): /source/blender/blenkernel/intern\object.c:3330 ob_parbone: Object Empty with Bone parent: bone doesn't exist ``` Now skip creation of a depsgraph relation if the Parent Bone field is empty (since this would be invalid anyways). ref. T91101 Maniphest Tasks: T91101 Differential Revision: https://developer.blender.org/D12389