code: private Integer getBatchSize(Method method) {
      // Determine queue batch size, if any
      Batch batch = method.getAnnotation(Batch.class);
      if (batch != null) {
        int batchSize = batch.value();
        Preconditions.checkArgument(batchSize > 0, "Batch size should be > 0: %s", method.getName());
        return batchSize;
      }
      return null;
    }
docs: Returns the user specify batch size or {@code null} if not specified.