System Information
MacOS: Big Sir
Graphics card: Radeon Pro 560X 4 GB

Blender Version
Broken: 2.93.2 - 2.93.5

Short description of error
When trying to import a brush set with the Import Brush Sets add-on, the import fails with a python error (pasted below). Works fine on Windows. This was first reported to me by someone else, using Blender 2.93.5. I tested it using 2.93.2 and I also get the same error.

Exact steps for others to reproduce the error
Go to file > import > brush set. Then select your brushes and try to import.

From the log...

bpy.context.space_data.context = 'MATERIAL'
bpy.context.object.active_material.name = "box"
bpy.data.materials["box"].node_tree.nodes["Principled BSDF"].inputs[0].default_value = (0.139679, 0.8, 0.118893, 1)
bpy.data.materials["box"].node_tree.nodes["Principled BSDF"].inputs[0].default_value = (0.139679, 0.8, 0.118893, 1)
bpy.context.space_data.shading.type = 'RENDERED'
bpy.context.space_data.system_bookmarks_active = 2
Python: Traceback (most recent call last):

File "/Applications/Blender.app/Contents/Resources/2.93/scripts/addons/io_import_BrushSet.py", line 121, in execute
  LoadBrushSet(self.properties.filepath, self.properties.filename)
File "/Applications/Blender.app/Contents/Resources/2.93/scripts/addons/io_import_BrushSet.py", line 70, in LoadBrushSet
  for file in os.listdir(filepath):

NotADirectoryError: [Errno 20] Not a directory: '/Users/dannyb/Desktop/20 Grunge Brushes/dbc_g-brush_pk_01_br_01.png'

location: <unknown location>:-1

Python: Traceback (most recent call last):

File "/Applications/Blender.app/Contents/Resources/2.93/scripts/addons/io_import_BrushSet.py", line 121, in execute
  LoadBrushSet(self.properties.filepath, self.properties.filename)
File "/Applications/Blender.app/Contents/Resources/2.93/scripts/addons/io_import_BrushSet.py", line 70, in LoadBrushSet
  for file in os.listdir(filepath):

NotADirectoryError: [Errno 20] Not a directory: '/Users/dannyb/Desktop/20_Grunge_Brushes/dbc_g-brush_pk_01_br_01.png'

location: <unknown location>:-1

bpy.data.window_managers["WinMan"].addon_search = "brush"
bpy.data.window_managers["WinMan"].addon_support = {'TESTING'}
bpy.data.window_managers["WinMan"].addon_support = {'OFFICIAL'}
Python: Traceback (most recent call last):

File "/Applications/Blender.app/Contents/Resources/2.93/scripts/addons/io_import_BrushSet.py", line 121, in execute
  LoadBrushSet(self.properties.filepath, self.properties.filename)
File "/Applications/Blender.app/Contents/Resources/2.93/scripts/addons/io_import_BrushSet.py", line 70, in LoadBrushSet
  for file in os.listdir(filepath):

NotADirectoryError: [Errno 20] Not a directory: '/Users/dannyb/Desktop/20_Grunge_Brushes/dbc_g-brush_pk_01_br_01.png'

location: <unknown location>:-1

bpy.context.space_data.system_bookmarks_active = 2
Python: Traceback (most recent call last):

File "/Applications/Blender.app/Contents/Resources/2.93/scripts/addons/io_import_BrushSet.py", line 121, in execute
  LoadBrushSet(self.properties.filepath, self.properties.filename)
File "/Applications/Blender.app/Contents/Resources/2.93/scripts/addons/io_import_BrushSet.py", line 70, in LoadBrushSet
  for file in os.listdir(filepath):

NotADirectoryError: [Errno 20] Not a directory: '/Users/dannyb/Desktop/20_Grunge_Brushes/dbc_g-brush_pk_01_br_01.png'

location: <unknown location>:-1