code: void setIsoEntry(final Iso9660FileEntry entry) {
          if (null != this.entry) {
              throw new RuntimeException("Cannot change the underlying entry once it has been set");
          }
          if (null == entry) {
              throw new IllegalArgumentException("'entry' cannot be null");
          }
  
          this.entry = entry;
          this.type = (entry.isDirectory()) ? FileType.FOLDER : FileType.FILE;
      }
docs: Sets the Iso9660FileEntry that backs this FileObject. This method is package-private because IsoFileSystem
  pre-creates some directory entries when building the file index, and it needs to set the backing entry after the
  fact.