Change panic to multierror

builder/googlecompute/config.go

@@ -59,6 +59,8 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 		return nil, nil, err
 	}
 
+	var errs *packer.MultiError
+
 	// Set defaults.
 	if c.Network == "" {
 		c.Network = "default"
@@ -75,12 +77,11 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 	if c.ImageName == "" {
 		img, err := interpolate.Render("packer-{{timestamp}}", nil)
 		if err != nil {
-			panic(err)
-		}
-
-		// Default to packer-{{ unix timestamp (utc) }}
+			errs = packer.MultiErrorAppend(errs,
+				fmt.Errorf("Unable to parse image name: %s ", err))
 			c.ImageName = img
 		}
+	}
 
 	if c.InstanceName == "" {
 		c.InstanceName = fmt.Sprintf("packer-%s", uuid.TimeOrderedUUID())
@@ -102,7 +103,6 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 		c.Comm.SSHUsername = "root"
 	}
 
-	var errs *packer.MultiError
 	if es := c.Comm.Prepare(&c.ctx); len(es) > 0 {
 		errs = packer.MultiErrorAppend(errs, es...)
 	}