TypeError: can only concatenate list (not "NoneType") to list

Hi guys while trying to upload new COA I have received this error “TypeError: can only concatenate list (not “NoneType”) to list”, tried to search solution for this but couldn’t find anything reasonable.

Below is my error report traceback,

Form/Chart of Accounts Importer
Error Report
Traceback (most recent call last):
File “/home/frappe/benches/bench-version-12-2019-10-30/apps/frappe/frappe/app.py”, line 60, in application
response = frappe.api.handle()
File “/home/frappe/benches/bench-version-12-2019-10-30/apps/frappe/frappe/api.py”, line 55, in handle
return frappe.handler.handle()
File “/home/frappe/benches/bench-version-12-2019-10-30/apps/frappe/frappe/handler.py”, line 22, in handle
data = execute_cmd(cmd)
File “/home/frappe/benches/bench-version-12-2019-10-30/apps/frappe/frappe/handler.py”, line 61, in execute_cmd
return frappe.call(method, **frappe.form_dict)
File “/home/frappe/benches/bench-version-12-2019-10-30/apps/frappe/frappe/init.py”, line 1038, in call
return fn(*args, **newargs)
File “/home/frappe/benches/bench-version-12-2019-10-30/apps/erpnext/erpnext/accounts/doctype/chart_of_accounts_importer/chart_of_accounts_importer.py”, line 63, in get_coa
forest = build_forest(generate_data_from_csv(file_name))
File “/home/frappe/benches/bench-version-12-2019-10-30/apps/erpnext/erpnext/accounts/doctype/chart_of_accounts_importer/chart_of_accounts_importer.py”, line 117, in build_forest
path = return_parent(data, account_name)[::-1]
File “/home/frappe/benches/bench-version-12-2019-10-30/apps/erpnext/erpnext/accounts/doctype/chart_of_accounts_importer/chart_of_accounts_importer.py”, line 99, in return_parent
return [child] + return_parent(data, parent_account)
TypeError: can only concatenate list (not “NoneType”) to list
Request Data
“type”: “POST”,
“args”: {
“file_name”: “/private/files/Chart_of_Accounts_Importer Innosoft3c0f40.csv”,
“parent”: “All Accounts”,
“doctype”: “Chart of Accounts Importer”,
“is_root”: true
“headers”: {},
“error_handlers”: {},
“url”: “/api/method/erpnext.accounts.doctype.chart_of_accounts_importer.chart_of_accounts_importer.get_coa”
Response JSON

Not a programer so can’t understand it. But I think there is something wrong with parent account, because whenever I upload COA without any parent account it successfully uploads the file but afterwards when I click start import it gives error “Root Account must be a group”

Really need help on this trying to solve this for past 3 days and really frustrated. I can even share the COA csv file if someone requires.