Indulgences.mm consists of a sequence of null bytes and nothing else, and therefore, there is no useful data in the file that could be recovered by manual editing or scripting. If you are in the habit of making regular backups (a good idea, sometimes the hard drive fails, etc.), you may be able to recover the data from a backup. I have no idea what happened to create this kind of a file. Unless you disabled automatic backups that FreeMind writes, you might be able to find a backup copy of the mind...
FreeMind does not start
This is unlikely to be a FreeMind bug so I am closing the issue.
This is unlikely to be a FreeMInd bug so I am closing the issue.
Fatal error losing data "Can't move a node to one if its children" (Mac OS Sierra)
If this happens only with JRE 10, one option is to install FreeMind-Windows-Installer-1.0.1-max-java-installer-embedded.exe, provided one in on Windows. This has JRE embedded, to be used specifically with FreeMind.
Find and Replace (Ctrl+Fhift+F) not working (Windows 7)
Java shows a warning (Ubuntu, OpenJDK)