Issue Summary

Trello comments from users who are no longer members of the board are imported as anonymous.

Steps to Reproduce

1. Create a Trello board and add a user to the board.
2. The user to leave comments on cards.
3. Remove the user from the Trello board.
4. Import the board into Jira.
5. Comments made by the user are imported as anonymous

Expected Results

The user who left the comment should be preserved

Actual Results

Comments are imported as anonymous.

Workaround

Identify and add missing users back to the board.

1) Export the Trello board as JSON
2) Filter out unique username values from the comments in the JSON to get
the unique list of users who have left comments
3) Add any missing usernames to the Trello board
4) Migrate to Jira and enter their email addresses as users during the
migration