Issue with simple operator for purge all material slots

Question

I have issue with this line of code.

import bpy
for obj in bpy.data.collections['Import'].all_objects:
    obj.select_set(True)

    bpy.context.view_layer.objects.active = obj
    bpy.ops.object.material_slot_remove()

The code its working fine when I executed.

But after I made simple operator and button for this operation. And when I linked this code with button.
I get this alert 'NoneType' object has no attribute 'active_material_index' Full code bellow. I will be very grateful for helping resolving this issue

import collections
import bpy
IMPORT HANDLE
def Button_01(context):
scene=bpy.data.scenes["Scene"].name     
### SET ACTIVE COLLECTION###
collections = bpy.context.view_layer.layer_collection.children

for collection in collections:
     if collection.name == "Import":
        bpy.context.view_layer.active_layer_collection = collection

folder = Path(r"D:\import")
fbx_files = [f for f in folder.glob("**/*.fbx")]
for fbx_file in fbx_files:
    bpy.ops.object.select_all(action='DESELECT')
    bpy.ops.import_scene.fbx(filepath=str(fbx_file))
    print('HANDLE IMPORT')
for obj in bpy.context.scene.objects:
    if obj.name.lower().startswith(""):
        print("found")
        for child in obj.children:
            print(child.name)

    ###### CLEAR PARENTS ######
for obj in bpy.data.collections['Import'].all_objects:
        obj.select_set(True)
        bpy.context.view_layer.objects.active = obj
        bpy.ops.object.parent_clear(type='CLEAR_KEEP_TRANSFORM')


    ####  DELETED UN USED PARTS ###  ### ONLY FOR MESH BASED NAME ####
        collection_name = "Import"
        collection = bpy.data.collections[collection_name]
        meshes = set()

for obj in [o for o in collection.objects if o.type == 'EMPTY']:
    meshes.add( obj.data )
    bpy.data.objects.remove( obj )


def mesh_delete(name):
    for obj in bpy.context.scene.objects:
        if obj.name.startswith(f'{name}'):
            obj.select_set(True)
            bpy.data.objects.remove( obj ) 

mesh_delete('screwHead')
mesh_delete('washer')




### NAME CHANGING FROM SKU CODE TO MATERIAL ###  ### ONLY FOR SKU CODE BASED NAME ###     

def Change_name(old_name, new_name):
    for obj in bpy.data.collections['Import'].all_objects:
        bpy.ops.object.select_all(action='DESELECT')
        if obj.name.lower().startswith(old_name.lower()) :
            objects = bpy.context.scene.objects
            objName = f'{old_name}'
            obj.name = f'{new_name}'

### PURE MATERIAL SLOTS ###  
for obj in bpy.data.collections['Import'].all_objects:
    obj.select_set(True)
    bpy.context.view_layer.objects.active = obj
    bpy.context.object.active_material_index = 0
    bpy.ops.object.material_slot_remove()            



class SimpleOperator(bpy.types.Operator):
    bl_idname = "object.simple_operator"
    bl_label = "Import Handle"
def execute(self, context):
    Button_01(context)
    return {'FINISHED'}





MENU
class LayoutDemoPanel2(bpy.types.Panel):
    """Creates a Panel in the scene context of the properties editor"""
    bl_label = "DC Render Menu- Handle"
    bl_idname = "SCENE_PT_layout2"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = "scene"
def draw(self, context):
    layout = self.layout
    scene = context.scene

    # Big button
    layout.label(text="Import Handle:")
    row = layout.row()
    row.scale_y = 1.0
    row.operator("object.simple_operator", icon ="GHOST_ENABLED")               




def register():
    bpy.utils.register_class(LayoutDemoPanel2)
    bpy.utils.register_class(SimpleOperator)
def unregister():
    bpy.utils.unregister_class(LayoutDemoPanel2)
    bpy.utils.unregister_class(SimpleOperator)
if name == "main":
    register()