docs: @BetaApi
    public final Operation updateBackendBucket(
        String backendBucket, BackendBucket backendBucketResource, List<String> fieldMask) {
  
      UpdateBackendBucketHttpRequest request =
          UpdateBackendBucketHttpRequest.newBuilder()
              .setBackendBucket(backendBucket)
              .setBackendBucketResource(backendBucketResource)
              .addAllFieldMask(fieldMask)
              .build();
      return updateBackendBucket(request);
    }