Fix null-check issue.

Author: rkistner

packages/powersync-sdk-web/src/db/sync/SharedWebStreamingSyncImplementation.ts

@@ -24,8 +24,11 @@ class SharedSyncClientProvider extends AbstractSharedSyncClientProvider {
     super();
   }
 
-  async fetchCredentials(): Promise<PowerSyncCredentials> {
+  async fetchCredentials(): Promise<PowerSyncCredentials | null> {
     const credentials = await this.options.remote.getCredentials();
+    if (credentials == null) {
+      return null;
+    }
     /**
      * The credentials need to be serializable.
      * Users might extend [PowerSyncCredentials] to contain

packages/powersync-sdk-web/src/worker/sync/AbstractSharedSyncClientProvider.ts

@@ -4,7 +4,7 @@ import { PowerSyncCredentials, SyncStatusOptions } from '@journeyapps/powersync-
  * The client side port should provide these methods.
  */
 export abstract class AbstractSharedSyncClientProvider {
-  abstract fetchCredentials(): Promise<PowerSyncCredentials>;
+  abstract fetchCredentials(): Promise<PowerSyncCredentials | null>;
   abstract uploadCrud(): Promise<void>;
   abstract statusChanged(status: SyncStatusOptions): void;