How to advance export plugin resource

Question

I have created a plugin and there are some resources I'm trying to export which will be putting in a group

what I have tried (example):
in a_resource.gd

tool
extends Resource

const A_resource = preload("res://a_resource.gd") 
# This is used for other things in my script

func _get_property_list() -> Array:
    return [
        {
            name="Resource",
            type=TYPE_OBJECT,
            hint=PROPERTY_HINT_RESOURCE_TYPE,
            hint_string="A_resource" # or "res://a_resource.gd"
        }
    ]

in plugin.gd

tool
extends EditorPlugin

const A_resource = preload("res://a_resource.gd") 

func _enter_tree():
    var none_texture = StreamTexture.new()
    add_custom_type('A_resource', 'Resource', A_resource, none_texture)

func _exit_tree():
    remove_custom_type('A_resource')

It seems to be working, but actually, it's outputting an error and the resource will be showing up no matter what resource you are exporting.