Action to reproduce this error:

Make a query with "prop=imageinfo&iiprog=user|comment" as parameter to get the username and comment info from as a list like:

https://commons.wikimedia.org/w/api.php?action=query&titles=File:Politisches_System_Albaniens.JPG&prop=imageinfo&iiprop=user|comment&iilimit=max

This results in empty comment strings (-> "null") for all file versions which is wrong.

When viewing this page on the wiki:

https://commons.wikimedia.org/wiki/File:Politisches_System_Albaniens.JPG

there is at least one file upload comment at the last file version (#6). There should be a file comment for every old file version (file version #1 to #5) too which is missing via API call and in the wiki.

This bugs happens to other files with only one file versions too, other example:

https://commons.wikimedia.org/w/api.php?action=query&titles=File:Delegate_doing_research.jpg&prop=imageinfo&iiprop=user|comment&iilimit=max

comment: null

Wiki page call reveal:

https://commons.wikimedia.org/wiki/File:Delegate_doing_research.jpg

comment: "User created page with UploadWizard"