XML namespace error

This only happens with the version I installed via pip (which installed in ~/.local/bin). The one in my cloned git repo works fine. I didn't expect there to be a difference, but apparently there is.

Traceback (most recent call last):
  File "/home/reinoutn/.local/bin/dtlapse", line 8, in <module>
    sys.exit(main())
  File "/home/reinoutn/.local/lib/python3.8/site-packages/dtlapse/dtlapse.py", line 217, in main
    modversion = get_modversion(args.operation, keyframe_xmps[0])
  File "/home/reinoutn/.local/lib/python3.8/site-packages/dtlapse/dtlapse.py", line 60, in get_modversion
    history = find_history(ET.parse(f).getroot())
  File "/home/reinoutn/.local/lib/python3.8/site-packages/dtlapse/dtlapse.py", line 52, in find_history
    items = root[0][0].findall('darktable:history', ns)
NameError: name 'ns' is not defined

The xmp file that triggered this is attached. RPN_20200810_Kick-In_4846.NEF.xmp