[#266] Fix namespace config initialization

Don't use nil Namespaces map in case when file isn't provided or invalid

Signed-off-by: Denis Kirillov <d.kirillov@yadro.com>

cmd/s3-gw/app_settings.go

@@ -482,7 +482,7 @@ func fetchNamespacesConfig(l *zap.Logger, v *viper.Viper) NamespacesConfig {
 
 	nsConfig, err := readNamespacesConfig(v.GetString(cfgNamespacesConfig))
 	if err != nil {
-		l.Warn(logs.FailedToParseNamespacesConfig)
+		l.Warn(logs.FailedToParseNamespacesConfig, zap.Error(err))
 	}
 
 	defaultNamespacesNames := fetchDefaultNamespaces(l, v)
@@ -516,18 +516,21 @@ func fetchNamespacesConfig(l *zap.Logger, v *viper.Viper) NamespacesConfig {
 }
 
 func readNamespacesConfig(filepath string) (NamespacesConfig, error) {
+	nsConfig := NamespacesConfig{
+		Namespaces: make(Namespaces),
+	}
+
 	if filepath == "" {
-		return NamespacesConfig{}, nil
+		return nsConfig, nil
 	}
 
 	data, err := os.ReadFile(filepath)
 	if err != nil {
-		return NamespacesConfig{}, fmt.Errorf("failed to read namespace config '%s': %w", filepath, err)
+		return nsConfig, fmt.Errorf("failed to read namespace config '%s': %w", filepath, err)
 	}
 
-	var nsConfig NamespacesConfig
 	if err = json.Unmarshal(data, &nsConfig); err != nil {
-		return NamespacesConfig{}, fmt.Errorf("failed to parse namespace config: %w", err)
+		return nsConfig, fmt.Errorf("failed to parse namespace config: %w", err)
 	}
 
 	return nsConfig, nil