Getting null for findFileByIoFile randomly

I'm getting a KotlinNullPointerException in the return statement of the given code. Any idea what could be the reason? It happens randomly, and never happens when I have a debugging breakpoints in place. 

private fun getProjectOutFolder(): VirtualFile {
    val outFolder = File(project.basePath + File.separator + "out")
    logger.info("Creating out folder: $outFolder")
    if (outFolder.exists()) {
        val outFolderDeleted = outFolder.deleteRecursively()
        logger.info("deleting existing out folder: $outFolderDeleted")
    }
    val outFolderCreated = outFolder.mkdirs()
    logger.info("created out folder: $outFolderCreated")
    return localFileSystem.findFileByIoFile(outFolder)!!
}