TypeError raised when a subtest ends successfully #85
Description
When a subtest ends, the method result.addSubTest is called, even when no error is encountered. A TypeError is then raised, because the error is None. Here is the end of the stacktrace:
File "/opt/python-3.4.2/lib/python3.4/unittest/case.py", line 513, in _feedErrorsToResult
result.addSubTest(test.test_case, test, exc_info)
File "/home/jenkins/venv/0/lib/python3.4/site-packages/xmlrunner/result.py", line 245, in addSubTest
testinfo = _TestInfo(self, testcase, _TestInfo.ERROR, err, subTest=test)
File "/home/jenkins/venv/0/lib/python3.4/site-packages/xmlrunner/result.py", line 102, in __init__
self.err, test_method)
File "/opt/python-3.4.2/lib/python3.4/unittest/result.py", line 173, in _exc_info_to_string
exctype, value, tb = err
TypeError: 'NoneType' object is not iterable
Hence, the error must be converted to string only if it is not None (https://hg.python.org/cpython/file/0be7c8f46378/Lib/unittest/result.py#l127).