private @NotNull FSItem convertAndCheck(@NotNull VirtualFile file) {
    FSItem fsItem = convert(file);
    if (fsItem == null) {
      //MAYBE RC: NoSuchFileException seems to fit better:
      // 1. it is an IOException -- no need to catch out-of-nothing IllegalStateException (see LightPlatformTestCase.tearDownSourceRoot())
      // 2. it is thrown by LocalFileSystemBase in case there is no such file -- more unified
      throw new IllegalStateException("Does not exist: " + file.getPath());
    }
    return fsItem;
  }
private @NotNull FSItem convertAndCheck(@NotNull VirtualFile file)