fix: UOM handling for transaction without item (#31389)

If invoice is made without item code then UOM, Stock UOM and
conversion_factor all need to be manually added, this is confusing and
leads missing them out leads to errors.

Simplest solution:

- if either UOM exists then set both to same uom conversion factor to
- also set conversion factor based on UOM conversions

erpnext/accounts/doctype/purchase_invoice/test_purchase_invoice.py

@@ -1616,6 +1616,26 @@ class TestPurchaseInvoice(unittest.TestCase, StockTestMixin):
 		company.enable_provisional_accounting_for_non_stock_items = 0
 		company.save()
 
+	def test_item_less_defaults(self):
+
+		pi = frappe.new_doc("Purchase Invoice")
+		pi.supplier = "_Test Supplier"
+		pi.company = "_Test Company"
+		pi.append(
+			"items",
+			{
+				"item_name": "Opening item",
+				"qty": 1,
+				"uom": "Tonne",
+				"stock_uom": "Kg",
+				"rate": 1000,
+				"expense_account": "Stock Received But Not Billed - _TC",
+			},
+		)
+
+		pi.save()
+		self.assertEqual(pi.items[0].conversion_factor, 1000)
+
 
 def check_gl_entries(doc, voucher_no, expected_gle, posting_date):
 	gl_entries = frappe.db.sql(

erpnext/controllers/accounts_controller.py

@@ -46,6 +46,7 @@ from erpnext.controllers.print_settings import (
 from erpnext.controllers.sales_and_purchase_return import validate_return
 from erpnext.exceptions import InvalidCurrency
 from erpnext.setup.utils import get_exchange_rate
+from erpnext.stock.doctype.item.item import get_uom_conv_factor
 from erpnext.stock.doctype.packed_item.packed_item import make_packing_list
 from erpnext.stock.get_item_details import (
 	_get_item_tax_template,
@@ -548,6 +549,15 @@ class AccountsController(TransactionBase):
 					if ret.get("pricing_rules"):
 						self.apply_pricing_rule_on_items(item, ret)
 						self.set_pricing_rule_details(item, ret)
+				else:
+					# Transactions line item without item code
+
+					uom = item.get("uom")
+					stock_uom = item.get("stock_uom")
+					if bool(uom) != bool(stock_uom):  # xor
+						item.stock_uom = item.uom = uom or stock_uom
+
+					item.conversion_factor = get_uom_conv_factor(item.get("uom"), item.get("stock_uom"))
 
 			if self.doctype == "Purchase Invoice":
 				self.set_expense_account(for_validate)