WIP: Strengthen helm release result by adding nil check

README.md

@@ -16,6 +16,7 @@ To change image tag of `smiling-penguin` release:
 helm update-config "cf.20190214.142635" --set-value image.tag=stable,kube.diego_cell_size=1
 helm update-config "cf.20190214.142635" --values file_path1
 helm update-config "cf.20190214.142635" --set-value image.tag=stable --values=file_path1
+helm  --tls --tls-ca-cert /tmp/helm_secret/ca.cert.pem --tls-cert /tmp/helm_secret/helm.cert.pem --tls-key /tmp/helm_secret/helm.key.pem update-config "cf.20190909.143636" --set-value sizing.diego_cell.count="1",kube.diego_cell_size="1"
 ```
 
 For the last sample command, the plugin will merge the key/value pairs specified in both --set-value and --value file, if there are different keys specified in both --set-value and --value file, then --set-value will override the value in --value file.

updatecfg.go

@@ -169,6 +169,18 @@ func (cmd *updateConfigCommand) run() error {
 		return err
 	}
 
+	if ls == nil {
+		return errors.New("[ERROR] Release list is nil.")
+	}
+
+	if len(ls.Releases) == 0 {
+		return errors.New("[ERROR] Release list is none.")
+	}
+
+	if ls.Releases[0].Config == nil {
+		return errors.New("[ERROR] Release config is nil.")
+	}
+
 	var preVals map[string]interface{}
 	err = yaml.Unmarshal([]byte(ls.Releases[0].Config.Raw), &preVals)
 	if err != nil {