Fix file diff not showing for directories

When using diff on a document, after editing the file, the diff is not showing all the changes, and sometimes comes with the fields empty

How to reproduce

• install web-ui
• create a note filling all the metadata
• edit by removing the nature field, save
• edit again by adding at leats 3 subjects
• click on compare icon
• (not all the subjects are shown after comparing 2 versions and not all the metadata is compared) error

Also sometimes the fields are just empty, with no data