on my system, on a clean master, I'm hitting the following error:

Traceback (most recent call last):
                       File "/home/gregs/code/pants/.pants.d/lint/pythonstyle/checker/f056857f828f95f73143d5abef284733401993e1-DefaultFingerprintStrategy.946276fa33a5/CPython-3.7.3/.bootstrap/pex/pex.py", line 356, in execute
                         self.patch_sys(pex_inherit_path)
                       File "/home/gregs/code/pants/.pants.d/lint/pythonstyle/checker/f056857f828f95f73143d5abef284733401993e1-DefaultFingerprintStrategy.946276fa33a5/CPython-3.7.3/.bootstrap/pex/pex.py", line 285, in patch_sys
                         new_sys_path, new_sys_path_importer_cache, new_sys_modules = self.minimum_sys(inherit_path)
                       File "/home/gregs/code/pants/.pants.d/lint/pythonstyle/checker/f056857f828f95f73143d5abef284733401993e1-DefaultFingerprintStrategy.946276fa33a5/CPython-3.7.3/.bootstrap/pex/pex.py", line 259, in minimum_sys
                         sys_modules = cls.minimum_sys_modules(site_libs)
                       File "/home/gregs/code/pants/.pants.d/lint/pythonstyle/checker/f056857f828f95f73143d5abef284733401993e1-DefaultFingerprintStrategy.946276fa33a5/CPython-3.7.3/.bootstrap/pex/pex.py", line 179, in minimum_sys_modules
                         if cls._tainted_path(module_file, site_libs):
                       File "/home/gregs/code/pants/.pants.d/lint/pythonstyle/checker/f056857f828f95f73143d5abef284733401993e1-DefaultFingerprintStrategy.946276fa33a5/CPython-3.7.3/.bootstrap/pex/pex.py", line 157, in _tainted_path
                         paths = frozenset([path, os.path.realpath(path)])
                       File "/home/gregs/code/pants/build-support/pants_dev_deps.py37.venv/lib/python3.7/posixpath.py", line 394, in realpath
                         filename = os.fspath(filename)
                     TypeError: expected str, bytes or os.PathLike object, not NoneType
                     
FAILURE: 1 Python Style issues found. You may try `./pants fmt <targets>`