fix: Conversion factor error for invoices without item code (petty expenses) (#32714)

* fix: Set default uom conversion factor to 1 for invoices

* chore: set default conversion_factor as 1

* chore: remove print statements
diff --git a/erpnext/accounts/doctype/sales_invoice_item/sales_invoice_item.json b/erpnext/accounts/doctype/sales_invoice_item/sales_invoice_item.json
index 62c3ced..35d19ed 100644
--- a/erpnext/accounts/doctype/sales_invoice_item/sales_invoice_item.json
+++ b/erpnext/accounts/doctype/sales_invoice_item/sales_invoice_item.json
@@ -890,7 +890,7 @@
  "idx": 1,
  "istable": 1,
  "links": [],
- "modified": "2022-11-02 12:53:12.693217",
+ "modified": "2022-12-28 16:17:33.484531",
  "modified_by": "Administrator",
  "module": "Accounts",
  "name": "Sales Invoice Item",
diff --git a/erpnext/controllers/accounts_controller.py b/erpnext/controllers/accounts_controller.py
index 334a2d8..788dc49 100644
--- a/erpnext/controllers/accounts_controller.py
+++ b/erpnext/controllers/accounts_controller.py
@@ -584,7 +584,12 @@
 					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"))
+					# UOM cannot be zero so substitute as 1
+					item.conversion_factor = (
+						get_uom_conv_factor(item.get("uom"), item.get("stock_uom"))
+						or item.get("conversion_factor")
+						or 1
+					)
 
 			if self.doctype == "Purchase Invoice":
 				self.set_expense_account(for_validate)