this is actually failing with buildout 3.0.1+slapos007:

While:
  Installing pillow-python.

An internal error occurred due to a bug in either zc.buildout or in a
recipe being used:
Traceback (most recent call last):
  File "eggs/zc.buildout-3.0.1+slapos007-py3.9.egg/zc/buildout/buildout.py", line 2664, in main
    getattr(buildout, command)(args)
  File "eggs/zc.buildout-3.0.1+slapos007-py3.9.egg/zc/buildout/buildout.py", line 855, in install
    self._install_parts(install_args)
  File "eggs/zc.buildout-3.0.1+slapos007-py3.9.egg/zc/buildout/buildout.py", line 1026, in _install_parts
    installed_files = self[part]._call(recipe.install)
  File "eggs/zc.buildout-3.0.1+slapos007-py3.9.egg/zc/buildout/buildout.py", line 1948, in _call
    return f()
  File "eggs/zc.recipe.egg-2.0.8.dev0+slapos007-py3.9.egg/zc/recipe/egg/custom.py", line 80, in install
    return self._install()
  File "eggs/zc.recipe.egg-2.0.8.dev0+slapos007-py3.9.egg/zc/recipe/egg/custom.py", line 150, in _install
    return zc.buildout.easy_install.build(
  File "eggs/zc.buildout-3.0.1+slapos007-py3.9.egg/zc/buildout/easy_install.py", line 1163, in build
    return installer.build(spec, build_ext, patch_dict=patch_dict)
  File "eggs/zc.buildout-3.0.1+slapos007-py3.9.egg/zc/buildout/easy_install.py", line 970, in build
    patch_dict = patch_dict[dist.project_name]
KeyError: 'pillow'