fix(core): only try to retrieve transferred state on the browser

Prior to this commit we tried to retrieve transferred state on both browser and server. Doing this on the server was redundant and could causes issues as `document` might be undefined.

Closes angular#50138

packages/core/src/transfer_state.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {APP_ID} from './application_tokens';
+import {APP_ID, PLATFORM_ID} from './application_tokens';
 import {inject} from './di/injector_compatibility';
 import {ɵɵdefineInjectable} from './di/interface/defs';
 import {getDocument} from './render3/interfaces/document';
@@ -72,7 +72,10 @@ export function makeStateKey<T = void>(key: string): StateKey<T> {
 
 function initTransferState() {
   const transferState = new TransferState();
-  transferState.store = retrieveTransferredState(getDocument(), inject(APP_ID));
+  if (inject(PLATFORM_ID) === 'browser') {
+    transferState.store = retrieveTransferredState(getDocument(), inject(APP_ID));
+  }
+
   return transferState;
 }
 
@@ -165,18 +168,18 @@ export class TransferState {
   }
 }
 
-function retrieveTransferredState(doc: Document, appId: string) {
+function retrieveTransferredState(doc: Document, appId: string): {[k: string]: unknown|undefined} {
   // Locate the script tag with the JSON data transferred from the server.
   // The id of the script tag is set to the Angular appId + 'state'.
   const script = doc.getElementById(appId + '-state');
-  let initialState = {};
-  if (script && script.textContent) {
+  if (script?.textContent) {
     try {
       // Avoid using any here as it triggers lint errors in google3 (any is not allowed).
-      initialState = JSON.parse(unescapeTransferStateContent(script.textContent)) as {};
+      return JSON.parse(unescapeTransferStateContent(script.textContent)) as {};
     } catch (e) {
       console.warn('Exception while restoring TransferState for app ' + appId, e);
     }
   }
-  return initialState;
+
+  return {};
 }