prevent go panic when output not specified for build config

pkg/api/graph/test/bc-missing-output.yaml

@@ -0,0 +1,33 @@
+apiVersion: v1
+kind: BuildConfig
+metadata:
+  annotations:
+    openshift.io/generated-by: OpenShiftNewApp
+  creationTimestamp: 2015-11-18T14:41:17Z
+  labels:
+    app: gitauthtest
+    template: gitserver
+  name: gitauthtest
+  namespace: devproj
+  resourceVersion: "634"
+  selfLink: /oapi/v1/namespaces/devproj/buildconfigs/gitauthtest
+  uid: 6d487478-8e02-11e5-9cf2-3c970e88b00e
+spec:
+  output: {}
+  resources: {}
+  source:
+    git:
+      uri: http://gitserver-tokenauth.linux.xip.io/ruby-hello-world
+    sourceSecret:
+      name: builder-token-nbme5
+    type: Git
+  strategy:
+    sourceStrategy:
+      from:
+        kind: ImageStreamTag
+        name: ruby:latest
+        namespace: openshift
+    type: Source
+  triggers: []
+status:
+  lastVersion: 1

pkg/build/graph/analysis/bc_test.go

@@ -72,6 +72,16 @@ func TestPushableBuild(t *testing.T) {
 	}
 }
 
+func TestBuildConfigNoOutput(t *testing.T) {
+	g, _, err := osgraphtest.BuildGraph("../../../api/graph/test/bc-missing-output.yaml")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// we were getting go panics with nil refs cause output destinations are not required for BuildConfigs
+	buildedges.AddAllInputOutputEdges(g)
+}
+
 func TestCircularDeps(t *testing.T) {
 	g, _, err := osgraphtest.BuildGraph("../../../api/graph/test/circular.yaml")
 	if err != nil {

pkg/build/graph/edges.go

@@ -79,6 +79,9 @@ func imageRefNode(g osgraph.MutableUniqueGraph, ref *kapi.ObjectReference, bc *b
 
 // AddOutputEdges links the build config to its output image node.
 func AddOutputEdges(g osgraph.MutableUniqueGraph, node *buildgraph.BuildConfigNode) {
+	if node.BuildConfig.Spec.Output.To == nil {
+		return
+	}
 	out := imageRefNode(g, node.BuildConfig.Spec.Output.To, node.BuildConfig)
 	g.AddEdge(node, out, BuildOutputEdgeKind)
 }