Data from `ANNOTATION_COUNT` event does not contain count oo rmatch documentation

Using the following code: 

        const annotationManager = await previewFile.getAnnotationManager()
        annotationManager.registerEventListener(
          ({ data }) => {
            onTotalComments(data)
          },
          { listenOn: ['ANNOTATION_COUNT'] }
        )

As documented in this page, the data returned does not match what is expected. I would expect a number for the total number of comments. However, the returned value is `{ mentioned: undefined}`.

Thanks in advance!