Previously it would fail with:
PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: 'bonsai\\bim\\data\\cache\\988c190483ae6bab7cf6b00cee78694d.h5'
Approach in 358c834 didn't worked out because annotations are assigned to the drawing after assign_class and we can't check in assign_class whether it's going to be part of the drawing.
Noticed that added drawing camera was linked to the scene collection and after collector.assign it was linked to the 2 collections instead of just 1 - it's own drawing collection and the scene collection.
Apparently we can't trust `obj.data == None` to identify empties since in Blender there are empties that can use `bpy.types.Image` as their `obj.data`.
Andrej730