Specify customData structure for FirebaseStorageError type

Author: hsubox76

packages/firebase/index.d.ts

@@ -7620,7 +7620,9 @@ declare namespace firebase.storage {
   /**
    * An error returned by the Firebase Storage SDK.
    */
-  interface FirebaseStorageError extends FirebaseError {}
+  interface FirebaseStorageError extends FirebaseError {
+    customData: { serverResponse: string | null };
+  }
 
   interface StorageObserver<T> {
     next?: NextFn<T> | null;

packages/storage-types/index.d.ts

@@ -85,7 +85,9 @@ export interface UploadMetadata extends SettableMetadata {
   md5Hash?: string | null;
 }
 
-export interface FirebaseStorageError extends FirebaseError {}
+interface FirebaseStorageError extends FirebaseError {
+  customData: { serverResponse: string | null };
+}
 
 export interface StorageObserver<T> {
   next?: NextFn<T> | null;

packages/storage/src/implementation/error.ts

@@ -18,14 +18,13 @@ import { FirebaseError } from '@firebase/util';
 import { CONFIG_STORAGE_BUCKET_KEY } from './constants';
 
 export class FirebaseStorageError extends FirebaseError {
-  customData: { serverResponse: string | null };
+  customData: { serverResponse: string | null } = { serverResponse: null };
 
   constructor(code: Code, message: string) {
     super(prependCode(code), 'Firebase Storage: ' + message);
     // Without this, `instanceof FirebaseStorageError`, in tests for example,
     // returns false.
     Object.setPrototypeOf(this, FirebaseStorageError.prototype);
-    this.customData = { serverResponse: null };
   }
 
   codeEquals(code: Code): boolean {