Merge pull request #16571 from Thunderbottom/purchase-invoice-fix

fix(purchase_invoice): fix undefined variable
diff --git a/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.py b/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.py
index f2d5006..0dd716d 100644
--- a/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.py
+++ b/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.py
@@ -231,7 +231,7 @@
 					item.expense_account = warehouse_account[item.warehouse]["account"]
 				else:
 					item.expense_account = stock_not_billed_account
-			elif item.is_fixed_asset and d.pr_detail:
+			elif item.is_fixed_asset and item.pr_detail:
 				item.expense_account = asset_received_but_not_billed
 			elif not item.expense_account and for_validate:
 				throw(_("Expense account is mandatory for item {0}").format(item.item_code or item.item_name))