From 3e3be5e2a3096203643e273a94c2d65f3ee743d7 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Mon, 11 Aug 2014 21:55:47 -0700
Subject: [PATCH] config: only walk if non-nil

---
 config/config.go | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/config/config.go b/config/config.go
index b89ffcf29..102e18163 100644
--- a/config/config.go
+++ b/config/config.go
@@ -127,11 +127,13 @@ func (c *Config) Validate() error {
 		}
 
 		w := &interpolationWalker{F: fn}
-		if err := reflectwalk.Walk(v.Default, w); err == nil {
-			if interp {
-				errs = append(errs, fmt.Errorf(
-					"Variable '%s': cannot contain interpolations",
-					v.Name))
+		if v.Default != nil {
+			if err := reflectwalk.Walk(v.Default, w); err == nil {
+				if interp {
+					errs = append(errs, fmt.Errorf(
+						"Variable '%s': cannot contain interpolations",
+						v.Name))
+				}
 			}
 		}
 	}