fix(rbac): add proper empty page for RBAC plugin

plugins/rbac/src/components/Router.test.tsx

@@ -32,6 +32,10 @@ jest.mock('./CreateRole/EditRolePage', () => ({
   EditRolePage: () => <div>EditRole</div>,
 }));
 
+jest.mock('@backstage/core-components', () => ({
+  ErrorPage: jest.fn().mockImplementation(() => <div>Mocked ErrorPage</div>),
+}));
+
 jest.mock('@backstage/plugin-permission-react', () => ({
   RequirePermission: jest
     .fn()
@@ -67,6 +71,17 @@ describe('Router component', () => {
     expect(screen.queryByText('RBAC')).not.toBeInTheDocument();
   });
 
+  it('should render ErrorPage when rbac-backend plugin is disabled', () => {
+    configMock.getOptionalBoolean.mockReturnValueOnce(false);
+    render(
+      <MemoryRouter initialEntries={['/']}>
+        <Router />
+      </MemoryRouter>,
+    );
+
+    expect(screen.queryByText('Mocked ErrorPage')).toBeInTheDocument();
+  });
+
   it('renders RoleOverviewPage when path matches roleRouteRef', () => {
     render(
       <MemoryRouter initialEntries={['/roles/user/testns/testname']}>

plugins/rbac/src/components/Router.tsx

@@ -1,6 +1,7 @@
 import React from 'react';
 import { Route, Routes } from 'react-router-dom';
 
+import { ErrorPage } from '@backstage/core-components';
 import { configApiRef, useApi } from '@backstage/core-plugin-api';
 import { RequirePermission } from '@backstage/plugin-permission-react';
 
@@ -25,7 +26,13 @@ export const Router = ({ useHeader = true }: { useHeader?: boolean }) => {
   const isRBACPluginEnabled = config.getOptionalBoolean('permission.enabled');
 
   if (!isRBACPluginEnabled) {
-    return null;
+    return (
+      <ErrorPage
+        status="404"
+        statusMessage="Enable the RBAC backend plugin to use this feature."
+        additionalInfo="To enable RBAC, set `permission.enabled` to `true` in the app-config file."
+      />
+    );
   }
 
   return (