fix output from RawConfigParser.write and ConfigParser.write for None

values (http://bugs.python.org/issue7005)
(merged r84443 from the release27-mmaint branch, with changes to reflect
changes in Python 3)

Lib/test/test_cfgparser.py

@@ -755,6 +755,34 @@ class SafeConfigParserTestCaseTrickyFile(CfgParserTestCaseClass):
         with self.assertRaises(UnicodeDecodeError):
             cf.read(tricky, encoding='ascii')
 
+
+class Issue7005TestCase(unittest.TestCase):
+    """Test output when None is set() as a value and allow_no_value == False.
+
+    http://bugs.python.org/issue7005
+
+    """
+
+    expected_output = "[section]\noption = None\n\n"
+
+    def prepare(self, config_class):
+        # This is the default, but that's the point.
+        cp = config_class(allow_no_value=False)
+        cp.add_section("section")
+        cp.set("section", "option", None)
+        sio = io.StringIO()
+        cp.write(sio)
+        return sio.getvalue()
+
+    def test_none_as_value_stringified(self):
+        output = self.prepare(configparser.ConfigParser)
+        self.assertEqual(output, self.expected_output)
+
+    def test_none_as_value_stringified_raw(self):
+        output = self.prepare(configparser.RawConfigParser)
+        self.assertEqual(output, self.expected_output)
+
+
 class SortedTestCase(RawConfigParserTestCase):
     dict_type = SortedDict
 
@@ -811,6 +839,7 @@ def test_main():
         SafeConfigParserTestCaseNoValue,
         SafeConfigParserTestCaseTrickyFile,
         SortedTestCase,
+        Issue7005TestCase,
         StrictTestCase,
         CompatibleTestCase,
         )