From f4ea1721783679b864d08b8d0485997ac04f0f50 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sat, 20 Apr 2013 19:08:10 -0600
Subject: [PATCH] NilBuilderFactory

---
 packer/build.go       | 7 +++++++
 packer/environment.go | 1 +
 2 files changed, 8 insertions(+)

diff --git a/packer/build.go b/packer/build.go
index 2e3ddf2e5..8d6cb1a60 100644
--- a/packer/build.go
+++ b/packer/build.go
@@ -31,3 +31,10 @@ type Builder interface {
 type BuilderFactory interface {
 	CreateBuilder(name string) Builder
 }
+
+// This implements BuilderFactory to return nil for every builder.
+type NilBuilderFactory byte
+
+func (NilBuilderFactory) CreateBuilder(name string) Builder {
+	return nil
+}
diff --git a/packer/environment.go b/packer/environment.go
index 021520dc2..a0f7dad42 100644
--- a/packer/environment.go
+++ b/packer/environment.go
@@ -51,6 +51,7 @@ type EnvironmentConfig struct {
 // be used to create a new enviroment with NewEnvironment with sane defaults.
 func DefaultEnvironmentConfig() *EnvironmentConfig {
 	config := &EnvironmentConfig{}
+	config.BuilderFactory = new(NilBuilderFactory)
 	config.Ui = &ReaderWriterUi{os.Stdin, os.Stdout}
 	return config
 }