From 7eacacbff288b1f1fcf4ed32d2fbafb7e668c75e Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Mon, 23 Jun 2014 12:32:04 -0700
Subject: [PATCH] terraform: MergeDiff can take nil diff

---
 terraform/state.go      | 14 ++++++++------
 terraform/state_test.go | 19 +++++++++++++++++++
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/terraform/state.go b/terraform/state.go
index 930ac7e74..ddb9c307b 100644
--- a/terraform/state.go
+++ b/terraform/state.go
@@ -131,13 +131,15 @@ func (s *ResourceState) MergeDiff(d *ResourceDiff) *ResourceState {
 			result.Attributes[k] = v
 		}
 	}
-	for k, diff := range d.Attributes {
-		if diff.NewComputed {
-			result.Attributes[k] = config.UnknownVariableValue
-			continue
-		}
+	if d != nil {
+		for k, diff := range d.Attributes {
+			if diff.NewComputed {
+				result.Attributes[k] = config.UnknownVariableValue
+				continue
+			}
 
-		result.Attributes[k] = diff.New
+			result.Attributes[k] = diff.New
+		}
 	}
 
 	return &result
diff --git a/terraform/state_test.go b/terraform/state_test.go
index e3f24b3ec..b6edcae40 100644
--- a/terraform/state_test.go
+++ b/terraform/state_test.go
@@ -70,6 +70,25 @@ func TestResourceState_MergeDiff_nil(t *testing.T) {
 	}
 }
 
+func TestResourceState_MergeDiff_nilDiff(t *testing.T) {
+	rs := ResourceState{
+		ID: "foo",
+		Attributes: map[string]string{
+			"foo": "bar",
+		},
+	}
+
+	rs2 := rs.MergeDiff(nil)
+
+	expected := map[string]string{
+		"foo": "bar",
+	}
+
+	if !reflect.DeepEqual(expected, rs2.Attributes) {
+		t.Fatalf("bad: %#v", rs2.Attributes)
+	}
+}
+
 func TestReadWriteState(t *testing.T) {
 	state := &State{
 		Resources: map[string]*ResourceState{