It was failing on Windows with something like "ValueError: path is on mount 'L:', start on mount 'C:'".
I guess it doesn't really occur in bonsai as sheets are typically stored next to the titleblocks (we used to use absolute paths awhile ago and now everything is relative to the ifc project)
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