fill up cpu memory if config is missing

cmd/minikube/cmd/start_flags.go

@@ -392,9 +392,6 @@ func updateExistingConfigFromFlags(cmd *cobra.Command, existing *config.ClusterC
 
 	cc := *existing
 
-	// validate the memory size in case user changed their system memory limits (example change docker desktop or upgraded memory.)
-	validateMemorySize(cc.Memory, cc.Driver)
-
 	if cmd.Flags().Changed(containerRuntime) {
 		cc.KubernetesConfig.ContainerRuntime = viper.GetString(containerRuntime)
 	}
@@ -411,19 +408,34 @@ func updateExistingConfigFromFlags(cmd *cobra.Command, existing *config.ClusterC
 		cc.MinikubeISO = viper.GetString(isoURL)
 	}
 
+	if cc.Memory == 0 {
+		glog.Info("Existing config file was missing memory. (could be an old minikube config), will use the default value")
+		memInMB, err := pkgutil.CalculateSizeInMB(viper.GetString(memory))
+		if err != nil {
+			glog.Warningf("error calculate memory size in mb : %v", err)
+		}
+		cc.Memory = memInMB
+	}
+
 	if cmd.Flags().Changed(memory) {
 		memInMB, err := pkgutil.CalculateSizeInMB(viper.GetString(memory))
 		if err != nil {
 			glog.Warningf("error calculate memory size in mb : %v", err)
 		}
-		if memInMB != existing.Memory {
+		if memInMB != cc.Memory {
 			out.WarningT("You cannot change the memory size for an exiting minikube cluster. Please first delete the cluster.")
 		}
-
 	}
 
+	// validate the memory size in case user changed their system memory limits (example change docker desktop or upgraded memory.)
+	validateMemorySize(cc.Memory, cc.Driver)
+
+	if cc.CPUs == 0 {
+		glog.Info("Existing config file was missing cpu. (could be an old minikube config), will use the default value")
+		cc.CPUs = viper.GetInt(cpus)
+	}
 	if cmd.Flags().Changed(cpus) {
-		if viper.GetInt(cpus) != existing.CPUs {
+		if viper.GetInt(cpus) != cc.CPUs {
 			out.WarningT("You cannot change the CPUs for an existing minikube cluster. Please first delete the cluster.")
 		}
 	}