fix(selling): guard proforma against unsubmitted SO and missing PDF

Address review findings:
- make_proforma_invoice: reject a non-submitted Sales Order (the whitelisted
  endpoint was previously only JS-gated on docstatus)
- send_proforma_email: throw a clear error when the attached PDF File is missing
  instead of passing a null fid to sendmail

erpnext/selling/doctype/proforma_invoice/proforma_invoice.py

@@ -152,6 +152,8 @@ def make_proforma_invoice(
 	validate_feature_enabled()
 	selected = frappe.parse_json(items)
 	sales_order_doc = frappe.get_doc("Sales Order", sales_order)
+	if sales_order_doc.docstatus != 1:
+		frappe.throw(_("A Proforma Invoice can only be created against a submitted Sales Order."))
 	so_items = {item.name: item for item in sales_order_doc.items}
 
 	proforma = frappe.new_doc("Proforma Invoice")
@@ -214,6 +216,8 @@ def send_proforma_email(proforma_name: str, recipients: str) -> None:
 		frappe.throw(_("This Proforma Invoice has no PDF to send."))
 
 	file_name = frappe.db.get_value("File", {"file_url": proforma.proforma_pdf}, "name")
+	if not file_name:
+		frappe.throw(_("The attached PDF file could not be found."))
 	frappe.sendmail(
 		recipients=[email.strip() for email in recipients.split(",") if email.strip()],
 		subject=_("Proforma Invoice {0}").format(proforma.name),

erpnext/selling/doctype/proforma_invoice/test_proforma_invoice.py

@@ -143,3 +143,14 @@ class TestProformaInvoice(ERPNextTestSuite):
 			sales_order,
 			[(sales_order.items[0].name, 4)],
 		)
+
+	def test_requires_submitted_sales_order(self):
+		"""The server rejects a proforma against a draft Sales Order (the button is JS-gated only)."""
+		sales_order = make_sales_order(qty=10, do_not_submit=True)
+
+		self.assertRaises(
+			frappe.ValidationError,
+			self.create_proforma,
+			sales_order,
+			[(sales_order.items[0].name, 4)],
+		)