From 1aea3512a4af8ea5423e3d625dc19386fee51a73 Mon Sep 17 00:00:00 2001
From: Chris Lu <chris.lu@gmail.com>
Date: Wed, 20 Mar 2013 01:23:15 -0700
Subject: [PATCH] return nil instead of memory access error

---
 go/topology/volume_layout.go | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/go/topology/volume_layout.go b/go/topology/volume_layout.go
index f5c2e2360..0791bed20 100644
--- a/go/topology/volume_layout.go
+++ b/go/topology/volume_layout.go
@@ -43,7 +43,10 @@ func (vl *VolumeLayout) isWritable(v *storage.VolumeInfo) bool {
 }
 
 func (vl *VolumeLayout) Lookup(vid storage.VolumeId) []*DataNode {
-	return vl.vid2location[vid].list
+  if location := vl.vid2location[vid]; location != nil {
+    return location.list
+  }
+	return nil
 }
 
 func (vl *VolumeLayout) PickForWrite(count int) (*storage.VolumeId, int, *VolumeLocationList, error) {