Guard against nil panics

cmd/minikube/cmd/start.go

@@ -155,7 +155,9 @@ func runStart(cmd *cobra.Command, args []string) {
 		exit.WithCodeT(exit.Data, "Unable to load config: {{.error}}", out.V{"error": err})
 	}
 
-	upgradeExistingConfig(existing)
+	if existing != nil {
+		upgradeExistingConfig(existing)
+	}
 
 	validateSpecifiedDriver(existing)
 	validateKubernetesVersion(existing)

cmd/minikube/cmd/start_flags.go

@@ -359,6 +359,10 @@ func generateClusterConfig(cmd *cobra.Command, existing *config.ClusterConfig, k
 
 // upgradeExistingConfig upgrades legacy configuration files
 func upgradeExistingConfig(cc *config.ClusterConfig) {
+	if cc == nil {
+		return
+	}
+
 	if cc.VMDriver != "" && cc.Driver == "" {
 		glog.Infof("config upgrade: Driver=%s", cc.VMDriver)
 		cc.Driver = cc.VMDriver