* @see Project#isRootProject()
     */
    @Nonnull
    Path getRootDirectory();

    /**
     * Returns a proto session builder of this instance.
     */
    @Nonnull
    default Builder toBuilder() {
        try {
            return new Builder(
                    getUserProperties(), getSystemProperties(), getStartTime(), getTopDirectory(), getRootDirectory());
        } catch (IllegalStateException e) {