Update revalidatePath.mdx (#54631)

add if statement, because typescript throws error: revalidatePath require `string`, but `searchParams.get('path')` returns `string|null` type




Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>

docs/02-app/02-api-reference/04-functions/revalidatePath.mdx

@@ -41,14 +41,23 @@ export default async function submit() {
 ### Route Handler
 
 ```ts filename="app/api/revalidate/route.ts" switcher
-import { NextRequest, NextResponse } from 'next/server'
 import { revalidatePath } from 'next/cache'
+import { NextRequest, NextResponse } from 'next/server'
 
 export async function GET(request: NextRequest) {
   const path = request.nextUrl.searchParams.get('path')
+
+  if (path) {
     revalidatePath(path)
     return NextResponse.json({ revalidated: true, now: Date.now() })
   }
+
+  return NextResponse.json({
+    revalidated: false,
+    now: Date.now(),
+    message: 'Missing path to revalidate',
+  })
+}
 ```
 
 ```js filename="app/api/revalidate/route.js" switcher
@@ -57,7 +66,16 @@ import { revalidatePath } from 'next/cache'
 
 export async function GET(request) {
   const path = request.nextUrl.searchParams.get('path')
+
+  if (path) {
     revalidatePath(path)
     return NextResponse.json({ revalidated: true, now: Date.now() })
   }
+
+  return NextResponse.json({
+    revalidated: false,
+    now: Date.now(),
+    message: 'Missing path to revalidate',
+  })
+}
 ```