Avoid crash if configuration is nil (#538)

* Avoid crash if configuration is nil

* feedback review

* clone the config so that is immutable

server/plugin.go

@@ -420,29 +420,31 @@ func (p *Plugin) restart() {
 
 func (p *Plugin) generatePluginSecrets() error {
 	needSaveConfig := false
-	if p.configuration.WebhookSecret == "" {
+	cfg := p.getConfiguration().Clone()
+	if cfg.WebhookSecret == "" {
 		secret, err := generateSecret()
 		if err != nil {
 			return err
 		}
 
-		p.configuration.WebhookSecret = secret
+		cfg.WebhookSecret = secret
 		needSaveConfig = true
 	}
-	if p.configuration.EncryptionKey == "" {
+	if cfg.EncryptionKey == "" {
 		secret, err := generateSecret()
 		if err != nil {
 			return err
 		}
 
-		p.configuration.EncryptionKey = secret
+		cfg.EncryptionKey = secret
 		needSaveConfig = true
 	}
 	if needSaveConfig {
-		configMap, err := p.configuration.ToMap()
+		configMap, err := cfg.ToMap()
 		if err != nil {
 			return err
 		}
+		p.setConfiguration(cfg)
 		if appErr := p.API.SavePluginConfig(configMap); appErr != nil {
 			return appErr
 		}