diff --git a/purchase_request.py b/purchase_request.py
index 8c7dc4a77d..c8a8c3d85d 100644
--- a/purchase_request.py
+++ b/purchase_request.py
@@ -54,10 +54,10 @@ class PurchaseRequest(OSV):
     def get_purchase(self, cursor, user, ids, name, args, context=None):
         res = {}
         for request in self.browse(cursor, user, ids, context=context):
-            if request.purchase_line and request.purchase_line.purchase:
+            if request.purchase_line:
                 res[request.id] = request.purchase_line.purchase.id
             else:
-                res[request.id] = None
+                res[request.id] = False
         return res
 
     def get_state(self, cursor, user, ids, name, args, context=None):