Fix: TypeError Cannot Read Properties of Null (Reading 'auth') in Next.js
Dharmendra
10 min read
You've just pushed your Next.js app to Vercel. Everything works perfectly locally—authentication flows are smooth, your layouts render correctly, and the build completes without a hitch. Then Vercel hits you with:
This Next.js prerendering error for the _not-found page with auth is one of those frustrating issues that only surfaces in production. It passes all local checks but bombs on Vercel's static generation phase. Let's break down exactly why this happens and how to fix it properly.
The Problem — Build Fails on Vercel with Auth Read Error for _not-found
The error message is straightforward: somewhere in your code, you're trying to access .auth (or a nested property) on something that's null. The tricky part is when this happens.
Here's a typical scenario. You have a layout that fetches the current user session and passes auth data to child components:
// ❌ Broken: app/layout.tsximport { getServerSession } from "next-auth";import { authOptions } from "@/lib/auth";import { Header }
userName={session.user.name} // 💥 Crashes when session is null
userRole={session.user.role}
/>
{children}
</body>
</html>
);
}
Locally, this works because:
You're logged in during development
The dev server handles requests dynamically
The session exists when you test
But on Vercel during the build phase, Next.js prerenders the /_not-found page. There's no active request context, no cookies, no session—just static HTML generation. Your getServerSession() returns null, and null.user.name throws the TypeError.
The build output typically looks like this:
✓ Linting and checking validity of types
✓ Collecting page data
Generating static pages (0/8) [= ]
Error occurred prerendering page "/_not-found".
Read more: https://nextjs.org/docs/messages/prerender-error
TypeError: Cannot read properties of null (reading 'auth')
at RootLayout (/app/.next/server/app/layout.js:1:2345)
at renderToHTML (...)
✓ Generating static pages (8/8)
> Export encountered errors on following paths:
/_not-found/page: /_not-found
This issue has been documented in the Next.js community, including discussions on GitHub issue #65447, where developers encounter similar prerendering failures with various module access patterns.
Why This Happens — Static Generation Runs Without Session Context
To understand this bug, you need to understand how Next.js handles the _not-found page.
The _not-found Page is Special
In the App Router, not-found.tsx is a special file that renders when notFound() is called or when a route doesn't match. During the build process, Next.js prerenders this page to create a static fallback for 404 responses.
Here's the key insight: prerendering happens at build time, not request time. There are:
No cookies
No request headers
No session tokens
No authentication context
Any code that assumes a valid session during render will fail.
The Root Layout Trap
The _not-found page inherits your root layout. If that layout contains auth-dependent logic without null checks, the prerender fails:
Request Flow (Runtime):
User → Headers/Cookies → getServerSession() → session object → render
Build Flow (Static):
Build process → No context → getServerSession() → null → 💥 crash
This is the fundamental discrepancy between local development (always dynamic) and Vercel production builds (static where possible).
The Solution — Safe Navigation and Fallback States
The fix involves defensive coding patterns that account for null session states during static generation. Here are the approaches, ordered by preference.
Approach 1: Optional Chaining (Quick Fix)
The simplest fix is adding optional chaining (?.) to all session property access:
Approach 4: Dynamic Rendering for Auth-Heavy Layouts
If certain layouts require authentication context to function, force dynamic rendering:
// ✅ app/(dashboard)/layout.tsximport { getServerSession } from "next-auth";import { authOptions } from "@/lib/auth";import { redirect } from "next/navigation";// Force dynamic rendering - skip prerenderingexport const dynamic = "force-dynamic";export default async function DashboardLayout({ children,}: { children: React.ReactNode;}) { const session = await getServerSession(authOptions); if (!session) { redirect("/login"); } // Now session is guaranteed to exist or user is redirected return ( <div className="dashboard"> <Sidebar user={session.user} /> <main>{children}</main> </div> );}
With export const dynamic = 'force-dynamic', Next.js won't attempt to prerender these routes, avoiding the null session issue entirely.
Fixing the _not-found Page Specifically
Sometimes you need a dedicated not-found.tsx that handles the unauthenticated prerender case:
// ✅ app/not-found.tsximport Link from "next/link";// This page will be prerendered - no auth assumptions allowedexport default function NotFound() { return ( <div className="not-found-container"> <h1>404 - Page Not Found</h1> <p>The page you're looking for doesn't exist.</p> <Link href="/">Return Home</Link> </div> );}
Keep your not-found.tsx free of any auth-dependent logic. It will be prerendered statically and served as a fallback.
Prevention & Best Practices — Building Auth-Resilient Apps
Encountering this Next.js prerendering error once is enough. Here's how to prevent it from happening again.
1. Audit All Auth Access Points
Search your codebase for patterns that assume session existence:
Create wrapper components that handle the auth state:
// ✅ components/AuthGuard.tsximport { getServerSession } from "next-auth";import { authOptions } from "@/lib/auth";interface AuthGuardProps { children: React.ReactNode; fallback?: React.ReactNode;}export async function AuthGuard({ children, fallback = null }: AuthGuardProps) { const session = await getServerSession(authOptions); if (!session) { return <>{fallback}</>; } return <>{children}</>;}// Usage in layoutexport default function Layout({ children }) { return ( <html> <body> <AuthGuard fallback={<PublicHeader />}> <AuthenticatedHeader /> </AuthGuard> {children} </body> </html> );}
5. Test Your Build Locally
Before pushing to Vercel, run the production build locally:
npm run build
This runs the same static generation process that Vercel uses. Prerendering errors will surface here, saving you from failed deployments.
6. Document Auth Patterns in Your Team
Create a coding standard for auth handling:
// DOC: Auth Access Guidelines//// ❌ NEVER: Direct property access without null check// const userId = session.user.id;//// ✅ ALWAYS: Use optional chaining or guards// const userId = session?.user?.id;// if (!session) return <UnauthenticatedView />;//// 💡 PREFER: Use getSafeSession() helper for consistent handling
Key Takeaways
The _not-found page is prerendered at build time with no request context, cookies, or session data—any auth access will be null.
Optional chaining (?.) and nullish coalescing (??) are your first line of defense for auth property access.
Use force-dynamic for layouts that truly require auth, accepting that these routes won't benefit from static optimization.
Create a centralized safe-auth helper to standardize null handling across your codebase and make patterns consistent.
Always test npm run build locally before deploying to catch prerendering errors early.
Next Steps
Audit your codebase: Search for session. without optional chaining and getServerSession calls without null guards.
Create a getSafeSession() helper: Centralize your auth logic with proper typing and fallback values.
Review your layout hierarchy: Ensure your root layout and not-found.tsx don't assume authenticated state.
Add build testing to CI: Include npm run build in your pipeline to catch these errors before they hit production.
Read the related discussions: Check out GitHub issue #65447 for additional context and edge cases the community has encountered.
The pattern of "works locally, fails on Vercel" is almost always about the difference between dynamic and static rendering. Once you internalize that prerendering has no request context, these bugs become easy to spot and prevent.
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