add default distDir value back into index.server.ts

packages/nextjs/src/index.server.ts

@@ -93,8 +93,9 @@ function sdkAlreadyInitialized(): boolean {
 }
 
 function addServerIntegrations(options: NextjsOptions): void {
-  // This value is injected at build time, based on the output directory specified in the build config
-  const distDirName = (global as GlobalWithDistDir).__rewriteFramesDistDir__;
+  // This value is injected at build time, based on the output directory specified in the build config. Though a default
+  // is set there, we set it here as well, just in case something has gone wrong with the injection.
+  const distDirName = (global as GlobalWithDistDir).__rewriteFramesDistDir__ || '.next';
   // nextjs always puts the build directory at the project root level, which is also where you run `next start` from, so
   // we can read in the project directory from the currently running process
   const distDirAbsPath = path.resolve(process.cwd(), distDirName);