* @see #getRootDirectory()
     */
    @Nonnull
    Path getTopDirectory();

    /**
     * Gets the root directory of the session, which is the root directory for the top directory project.
     *
     * @return the root directory, never {@code null}
     * @throws IllegalStateException if the root directory could not be found
     * @see #getTopDirectory()
     * @see Project#getRootDirectory()
     * @see Project#isRootProject()