twine check against a distribution with no description fails with AttributeError

[asottile]

Your Environment

$ pip freeze --all
bleach==3.0.0
certifi==2018.8.24
cffi==1.11.5
chardet==3.0.4
cmarkgfm==0.4.2
docutils==0.14
future==0.16.0
idna==2.7
pip==18.1
pkginfo==1.4.2
pycparser==2.19
Pygments==2.2.0
readme-renderer==22.0
requests==2.19.1
requests-toolbelt==0.8.0
setuptools==40.4.3
six==1.11.0
tqdm==4.26.0
twine==1.12.1
urllib3==1.23
webencodings==0.5.1
wheel==0.32.1

$ twine --version
twine version 1.12.1 (pkginfo: 1.4.2, requests: 2.19.1, setuptools: 40.4.3,
requests-toolbelt: 0.8.0, tqdm: 4.26.0)

$ python --version --version
Python 3.6.5 (default, Apr  1 2018, 05:46:30) 
[GCC 7.3.0]

$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.1 LTS
Release:	18.04
Codename:	bionic

Steps to Reproduce

If the issue is predictable and consistently reproducible, please list the steps here.

setup.py

from setuptools import setup

setup(name='foo', version='0.0.0')

reproduction

$ python setup.py sdist >& /dev/null
$ twine check dist/*
Checking distribution dist/foo-0.0.0.tar.gz: Traceback (most recent call last):
  File "/tmp/t/venv/bin/twine", line 11, in <module>
    sys.exit(main())
  File "/tmp/t/venv/lib/python3.6/site-packages/twine/__main__.py", line 28, in main
    return dispatch(sys.argv[1:])
  File "/tmp/t/venv/lib/python3.6/site-packages/twine/cli.py", line 75, in dispatch
    return main(args.args)
  File "/tmp/t/venv/lib/python3.6/site-packages/twine/commands/check.py", line 126, in main
    return check(args.dists)
  File "/tmp/t/venv/lib/python3.6/site-packages/twine/commands/check.py", line 97, in check
    metadata.get("description"), stream=stream, **parameters
  File "/tmp/t/venv/lib/python3.6/site-packages/readme_renderer/rst.py", line 95, in render
    parts = publish_parts(raw, writer=writer, settings_overrides=settings)
  File "/tmp/t/venv/lib/python3.6/site-packages/docutils/core.py", line 450, in publish_parts
    enable_exit_status=enable_exit_status)
  File "/tmp/t/venv/lib/python3.6/site-packages/docutils/core.py", line 664, in publish_programmatically
    output = pub.publish(enable_exit_status=enable_exit_status)
  File "/tmp/t/venv/lib/python3.6/site-packages/docutils/core.py", line 217, in publish
    self.settings)
  File "/tmp/t/venv/lib/python3.6/site-packages/docutils/readers/__init__.py", line 71, in read
    self.input = self.source.read()
  File "/tmp/t/venv/lib/python3.6/site-packages/docutils/io.py", line 435, in read
    return self.decode(self.source)
  File "/tmp/t/venv/lib/python3.6/site-packages/docutils/io.py", line 99, in decode
    data_encoding = self.determine_encoding_from_data(data)
  File "/tmp/t/venv/lib/python3.6/site-packages/docutils/io.py", line 142, in determine_encoding_from_data
    if data.startswith(start_bytes):
AttributeError: 'NoneType' object has no attribute 'startswith'

[mithun]

@sigmavirus24 Can you please release the changes from #412 ?