Fix Error when Author is Null

[chrisjtang]

Description

Added some safeguards and default values if the Post's author is null.

Motivation and Context

#140

How Has This Been Tested?

Added unit test for comment_data_from_post function

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• All new and existing tests passed.