Fix BackupSubscriptionCheckJob tests.

libsignal-service/src/main/java/org/whispersystems/signalservice/api/NetworkResult.kt

@@ -246,6 +246,16 @@ sealed class NetworkResult<T>(
     }
   }
 
+  /**
+   * Returns the result if successful, otherwise null.
+   */
+  fun successOrNull(): T? {
+    return when (this) {
+      is Success -> result
+      else -> null
+    }
+  }
+
   /**
    * Returns the [Throwable] associated with the result, or null if the result is successful.
    */