Error report in POS and Invoice reported by multiple users

[umairsy]

Traceback (most recent call last): File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/app.py", line 56, in application response = frappe.handler.handle() File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/handler.py", line 21, in handle data = execute_cmd(cmd) File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/handler.py", line 52, in execute_cmd return frappe.call(method, **frappe.form_dict) File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/__init__.py", line 922, in call return fn(*args, **newargs) File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/desk/form/save.py", line 22, in savedocs doc.save() File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/model/document.py", line 230, in save return self._save(*args, **kwargs) File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/model/document.py", line 263, in _save self.run_before_save_methods() File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/model/document.py", line 772, in run_before_save_methods self.run_method("validate") File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/model/document.py", line 666, in run_method out = Document.hook(fn)(self, *args, **kwargs) File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/model/document.py", line 887, in composer return composed(self, method, *args, **kwargs) File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/model/document.py", line 870, in runner add_to_return_value(self, fn(self, *args, **kwargs)) File "/home/frappe/benches/bench-2017-07-27/apps/frappe/frappe/model/document.py", line 660, in fn = lambda self, *args, **kwargs: getattr(self, method)(*args, **kwargs) File "/home/frappe/benches/bench-2017-07-27/apps/erpnext/erpnext/accounts/doctype/sales_invoice/sales_invoice.py", line 56, in validate super(SalesInvoice, self).validate() File "/home/frappe/benches/bench-2017-07-27/apps/erpnext/erpnext/controllers/selling_controller.py", line 33, in validate super(SellingController, self).validate() File "/home/frappe/benches/bench-2017-07-27/apps/erpnext/erpnext/controllers/stock_controller.py", line 17, in validate super(StockController, self).validate() File "/home/frappe/benches/bench-2017-07-27/apps/erpnext/erpnext/controllers/accounts_controller.py", line 47, in validate self.validate_due_date() File "/home/frappe/benches/bench-2017-07-27/apps/erpnext/erpnext/controllers/accounts_controller.py", line 125, in validate_due_date validate_due_date(self.posting_date, self.due_date, "Customer", self.customer, self.company) File "/home/frappe/benches/bench-2017-07-27/apps/erpnext/erpnext/accounts/party.py", line 302, in validate_due_date default_due_date = get_due_date(posting_date, party_type, party, company) File "/home/frappe/benches/bench-2017-07-27/apps/erpnext/erpnext/accounts/party.py", line 267, in get_due_date credit_days_based_on, credit_days = get_credit_days(party_type, party, company) File "/home/frappe/benches/bench-2017-07-27/apps/erpnext/erpnext/accounts/party.py", line 287, in get_credit_days frappe.db.get_value("Customer Group", customer_group, ["credit_days_based_on", "credit_days"]) TypeError: 'NoneType' object is not iterable