Don't set default for warehouse when creating serial no
diff --git a/erpnext/stock/doctype/serial_no/serial_no.py b/erpnext/stock/doctype/serial_no/serial_no.py
index ff4d519..fe4af21 100644
--- a/erpnext/stock/doctype/serial_no/serial_no.py
+++ b/erpnext/stock/doctype/serial_no/serial_no.py
@@ -278,13 +278,16 @@
 
 def make_serial_no(serial_no, sle):
 	sr = frappe.new_doc("Serial No")
+	sr.warehouse = None
+	sr.dont_update_if_missing.append("warehouse")
 	sr.ignore_permissions = True
+
 	sr.serial_no = serial_no
 	sr.item_code = sle.item_code
-	sr.warehouse = None
 	sr.company = sle.company
 	sr.via_stock_ledger = True
 	sr.insert()
+
 	sr.warehouse = sle.warehouse
 	sr.status = "Available"
 	sr.save()