Your IDE is trying to hide your changes before it merges (pull = fetch + merge) and cannot do this.
This is something like this:
Tried to save uncommitted changes in stash but failed with an error.
The easiest way is to open git bash, check the status, and then save, add, or discard the changes.
A few notes:
Intellij has something internal called a shelf, similar to git stash, but the files are stored and processed by IntelliJ, not git, so pay attention to this if you decide to stash ( shelf ) in the IDE.
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