Required means the key is present; nullable means its value may be null. These are different. Examples are synthetic, complete for the documented fields, and not real customer data.
Comment text. Tagged users and teams appear as @ and their name, or @Unknown user / @Unknown team when the user or team no longer exists. null when the comment has no text, such as a voice, video or GIF comment.
Example "@Rep Rachel great discovery questions here"
The voice or video recording on this comment; null for a comment without one, including GIF comments, whose GIF is not exported. See CommentAttachment.