### Summary Commenting on lines that have no diffs on the `Changes` tab of MRs in the `Hide whitespace changes` mode (`?w=1`) does not work. However when commenting on a line where a diff is present it works correctly. ### Steps to reproduce - Create a merge request with a line of diff. - View it with `Hide whitespace changes` mode ~~(append `?w=1` at the end of the url)~~ - comment a line that was not impacted by the diff (in whitespace mode - but surely impacted in real) ### Expected behavior The comment should be saved. ### Actual behavior no comment is added to the merge request. ### Relevant logs and/or screenshots The api responds with ``` {"valid":false,"award":false,"errors":{"diff_line":["can't be blank"],"line_code":["can't be blank","must be a valid line code"]}} ```