From 3857822ef2741eb680b3d635af0f759f69d520a7 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sun, 19 Jan 2014 15:19:10 -0800
Subject: [PATCH] packer: don't crash if arg is empty [GH-832]

---
 CHANGELOG.md               | 1 +
 packer/environment.go      | 2 +-
 packer/environment_test.go | 7 +++++++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index dcb835f15..be793c167 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 BUG FIXES:
 
+* core: Fix crash case if blank parameters are given to Packer. [GH-832]
 * builders/docker: user variables work properly. [GH-777]
 * builder/virtualbox,vmware: iso\_checksum is not required if the
   checksum type is "none"
diff --git a/packer/environment.go b/packer/environment.go
index 34dd8ba7d..a7067a682 100644
--- a/packer/environment.go
+++ b/packer/environment.go
@@ -221,7 +221,7 @@ func (e *coreEnvironment) Cli(args []string) (result int, err error) {
 
 	// Trim up to the command name
 	for i, v := range args {
-		if v[0] != '-' {
+		if len(v) > 0 && v[0] != '-' {
 			args = args[i:]
 			break
 		}
diff --git a/packer/environment_test.go b/packer/environment_test.go
index b5ac7b9c8..65bc83057 100644
--- a/packer/environment_test.go
+++ b/packer/environment_test.go
@@ -198,10 +198,17 @@ func TestEnvironment_Cli_CallsRun(t *testing.T) {
 func TestEnvironment_DefaultCli_Empty(t *testing.T) {
 	defaultEnv := testEnvironment()
 
+	// Test with no args
 	exitCode, _ := defaultEnv.Cli([]string{})
 	if exitCode != 1 {
 		t.Fatalf("bad: %d", exitCode)
 	}
+
+	// Test with only blank args
+	exitCode, _ = defaultEnv.Cli([]string{""})
+	if exitCode != 1 {
+		t.Fatalf("bad: %d", exitCode)
+	}
 }
 
 func TestEnvironment_DefaultCli_Help(t *testing.T) {