diff --git a/ll.py b/ll.py
index bf20b96..81a9415 100644
--- a/ll.py
+++ b/ll.py
@@ -95,12 +95,14 @@ def ty2s(ty):
 
 
 def oper2s(operand):
-    if isinstance(operand, Const):
+    if isinstance(operand, Null):
+        return 'null'
+    elif isinstance(operand, Const):
         return str(operand.val)
-    elif isinstance(operand, Id):
-        return '%' + operand.val
     elif isinstance(operand, Gid):
         return '@' + operand.val
+    elif isinstance(operand, Id):
+        return '%' + operand.val
     else:
         # TODO
         print('oper2s: Unknown operand: {}'