New VersionConflict reporting breaks tests

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Originally reported by: jaraco (Bitbucket: jaraco, GitHub: jaraco)

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https://travis-ci.org/jaraco/setuptools/jobs/37692346

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• Bitbucket: https://bitbucket.org/pypa/setuptools/issue/270

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Original comment by msabramo (Bitbucket: msabramo, GitHub: msabramo):

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It took me a bit to reproduce this, so logging it here for future versions of ourselves:

 marca@marca-mac2.local ⮀ hg-repos/setuptools_better_VersionConflict_error ⮀
 ❯ tox -e py27 -- -k testResolve --tb=short setuptools/tests/test_resources.py
GLOB sdist-make: /Users/marca/dev/hg-repos/setuptools_better_VersionConflict_error/setup.py
py27 inst-nodeps: /Users/marca/dev/hg-repos/setuptools_better_VersionConflict_error/.tox/dist/setuptools-6.0.3dev.zip
py27 runtests: PYTHONHASHSEED='268221285'
py27 runtests: commands[0] | py.test -k testResolve --tb=short setuptools/tests/test_resources.py
============================================================================= test session starts ==============================================================================
platform darwin -- Python 2.7.6 -- py-1.4.25 -- pytest-2.6.3
collected 30 items

setuptools/tests/test_resources.py F

=================================================================================== FAILURES ===================================================================================
___________________________________________________________________________ DistroTests.testResolve ____________________________________________________________________________
setuptools/tests/test_resources.py:172: in testResolve
    parse_requirements("Foo==0.9"), ad)
.tox/py27/lib/python2.7/site-packages/pkg_resources.py:632: in resolve
    % (dist, req, list(required_by.get(req))))
E   TypeError: 'NoneType' object is not iterable
==================================================================== 29 tests deselected by '-ktestResolve' ====================================================================
=================================================================== 1 failed, 29 deselected in 0.17 seconds ====================================================================
ERROR: InvocationError: '/Users/marca/dev/hg-repos/setuptools_better_VersionConflict_error/.tox/py27/bin/py.test -k testResolve --tb=short setuptools/tests/test_resources.py'
___________________________________________________________________________________ summary ____________________________________________________________________________________
ERROR:   py27: commands failed

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Original comment by msabramo (Bitbucket: msabramo, GitHub: msabramo):

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@jaraco: Sorry about this. Take a look at https://bitbucket.org/pypa/setuptools/pull-request/91/fix-versionconflict-test-failure/diff

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Original comment by jaraco (Bitbucket: jaraco, GitHub: jaraco):

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Merge VersionConflict test failure. Fixes #270.

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Original comment by jaraco (Bitbucket: jaraco, GitHub: jaraco):

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Fix VersionConflict test failure

Fixes TypeError: 'NoneType' object is not iterable error at pkg_resources.py:632

Fixes issue #270