fix: handle bullet points in reference blocks

[PRESIDENT810]

If there's a reference block with bullet points only, this extension will fail to export:

Error message: Cannot read properties of undefined (reading 'rich_text')

Error code: 400

My prompt:

> - SEC Rule 606 requires broker-dealers to disclose routing practices for non-directed orders.  
> - Robinhood’s PFOF model has drawn scrutiny over potential conflicts of interest and order execution quality.
output the text above with nothing else