Tidy: Unhide allow-empty-selectors flag and hint to it in the error m…

…essage

cmd/file_namespace.go

@@ -59,7 +59,7 @@ func executeNamespace(cmd *cobra.Command, _ []string) error {
 
 	err = namespace.Apply(yamlNode, selectors, cmdNamespacePathPrefix, cmdNamespaceAllowEmptySelectors)
 	if err != nil {
-		return fmt.Errorf("failed to apply the namespace: %w", err)
+		return fmt.Errorf("failed to apply the namespace: %w. Use --allow-empty-selectors to suppress this error.", err)
 	}
 
 	data = jsonbasics.ConvertToJSONobject(yamlNode)
@@ -141,7 +141,6 @@ routes:
 		"The path based namespace to apply.")
 	namespaceCmd.Flags().BoolVarP(&cmdNamespaceAllowEmptySelectors, "allow-empty-selectors",
 		"", false, "do not error out if the selectors return empty")
-	namespaceCmd.Flags().Lookup("allow-empty-selectors").Hidden = true
 
 	return namespaceCmd
 }