public List<GFile> getListing(GFile directory) throws IOException {
		if (isClosed()) {
			throw new IOException("Invalid state, index already closed");
		}
		return directory == null || rootDir.equals(directory) ? List.of(payloadFile) : List.of();
	}
Mirrors {@link GFileSystem#getListing(GFile)} interface.

@param directory {@link GFile} directory to get the list of child files that have been
added to this index, null means root directory.
@return {@link List} of GFile files that are in the specified directory, never null.
@throws IOException if already closed.
Ghidra/Features/Base/src/main/java/ghidra/formats/gfilesystem/SingleFileSystemIndexHelper.java