refactor(examples/nextjs-app-optimistic-updates): apply post-review corrections

Author: Guilherme Rabelo

examples/react/nextjs-app-optimistic-updates/.eslintrc.cjs

@@ -6,7 +6,12 @@ export async function GET() {
 }
 
 export async function POST(request: Request) {
-  const body = (await request.json()) as unknown
+  let body: unknown
+  try {
+    body = await request.json()
+  } catch {
+    return NextResponse.json({ error: 'text is required' }, { status: 400 })
+  }
 
   const text =
     body !== null &&