Unable to create invoice from subscription

Hello,
Im trying to create an invoice from a subscription but i get:
Any ideas?

Traceback (most recent call last):
  File "/home/frappe/frappe-bench/apps/frappe/frappe/app.py", line 61, in application
    response = frappe.handler.handle()
  File "/home/frappe/frappe-bench/apps/frappe/frappe/handler.py", line 21, in handle
    data = execute_cmd(cmd)
  File "/home/frappe/frappe-bench/apps/frappe/frappe/handler.py", line 56, in execute_cmd
    return frappe.call(method, **frappe.form_dict)
  File "/home/frappe/frappe-bench/apps/frappe/frappe/__init__.py", line 1026, in call
    return fn(*args, **newargs)
  File "/home/frappe/frappe-bench/apps/erpnext/erpnext/accounts/doctype/subscription/subscription.py", line 502, in get_subscription_updates
    subscription.process()
  File "/home/frappe/frappe-bench/apps/erpnext/erpnext/accounts/doctype/subscription/subscription.py", line 311, in process
    self.process_for_active()
  File "/home/frappe/frappe-bench/apps/erpnext/erpnext/accounts/doctype/subscription/subscription.py", line 344, in process_for_active
    self.generate_invoice()
  File "/home/frappe/frappe-bench/apps/erpnext/erpnext/accounts/doctype/subscription/subscription.py", line 229, in generate_invoice
    invoice = self.create_invoice(prorate)
  File "/home/frappe/frappe-bench/apps/erpnext/erpnext/accounts/doctype/subscription/subscription.py", line 280, in create_invoice
    invoice.save()
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py", line 260, in save
    return self._save(*args, **kwargs)
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py", line 283, in _save
    self.insert()
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py", line 222, in insert
    self.run_before_save_methods()
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py", line 876, in run_before_save_methods
    self.run_method("validate")
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py", line 772, in run_method
    out = Document.hook(fn)(self, *args, **kwargs)
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py", line 1048, in composer
    return composed(self, method, *args, **kwargs)
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py", line 1031, in runner
    add_to_return_value(self, fn(self, *args, **kwargs))
  File "/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py", line 766, in <lambda>
    fn = lambda self, *args, **kwargs: getattr(self, method)(*args, **kwargs)
  File "/home/frappe/frappe-bench/apps/erpnext/erpnext/accounts/doctype/sales_invoice/sales_invoice.py", line 118, in validate
    self.set_against_income_account()
  File "/home/frappe/frappe-bench/apps/erpnext/erpnext/accounts/doctype/sales_invoice/sales_invoice.py", line 492, in set_against_income_account
    self.against_income_account = ','.join(against_acc)
TypeError: sequence item 0: expected string or Unicode, NoneType found

have you find any solution same issue wth me