What if opening an existing project with Intellij IDEA went wrong?

Try to delete the IDE’s project/workspace configuration files and reopen the project directory.

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rm -rf .idea # idea's workspace configuration directory
rm -rf *.iml # Java project file

Deleting these files won’t hurt your project, and be sure not to upload these files to your version control repository.

These files should be excluded from vcs, for local workspace configuration should be different for each user. If you submitted them to vcs, conflicts will occur.