If buildout needs to generate scripts, then this argument is required,
otherwise, there will be an error in buildout. The following happened with
python3.6 and zc.buildout 2.7.1+slapos001:

    Traceback (most recent call last):
      File "slapos.buildout/src/zc/buildout/buildout.py", line 2240, in main
        getattr(buildout, command)(args)
      File "slapos.buildout/src/zc/buildout/buildout.py", line 643, in install
        self._install_parts(install_args)
      File "slapos.buildout/src/zc/buildout/buildout.py", line 658, in _install_parts
        self._setup_directories()
      File "slapos.rebootstrap/slapos/rebootstrap/__init__.py", line 37, in wrapper
        return getattr(self, attr)(*args, **kw)
      File "slapos.rebootstrap/slapos/rebootstrap/__init__.py", line 72, in _setup_directories
        setup_script(new_bin, self.wanted_python)
      File "slapos.rebootstrap/slapos/rebootstrap/bootstrap.py", line 31, in setup_script
        python,
      File "slapos.buildout/src/zc/buildout/easy_install.py", line 1313, in scripts
        sname = os.path.join(dest, sname)
      File "python3/lib/python3.6/posixpath.py", line 80, in join
        a = os.fspath(a)
    TypeError: expected str, bytes or os.PathLike object, not NoneType