update changelog

CHANGELOG.md

@@ -13,6 +13,7 @@
 * builder/amazon-ebsvolume: Fix interpolation of block_device. [GH-4464]
 * builder/vmware: ESXi: VNC port timeout increased to 5 s. [GH-4480]
 * core: always check for an error first when walking a path. [GH-4467]
+* builder/virtualbox: remove guest additions before saving image. [GH-4496]
 
 ## 0.12.2 (January 20, 2017)
 

template/interpolate/funcs.go

@@ -138,12 +138,12 @@ func funcGenTimestamp(ctx *Context) interface{} {
 }
 
 func funcGenUser(ctx *Context) interface{} {
-	return func(k string) string {
+	return func(k string) (string, error) {
 		if ctx == nil || ctx.UserVariables == nil {
-			return ""
+			return "", errors.New("test")
 		}
 
-		return ctx.UserVariables[k]
+		return ctx.UserVariables[k], nil
 	}
 }