As the title says: File and folder name input isn't checked for invalid characters, which causes a file/folder with an invalid name to be attempted to be created, causing the game to crash with a java.nio.file.InvalidPathException error.

I would assume which characters are valid depends on the OS. On windows the following characters can't be used in file and folder paths: \ / : * ? " < > |

MCG-1.18-1.2.6