Index: Lib/ConfigParser.py
===================================================================
--- Lib/ConfigParser.py	(revision 84442)
+++ Lib/ConfigParser.py	(working copy)
@@ -400,7 +400,7 @@
             for (key, value) in self._sections[section].items():
                 if key == "__name__":
                     continue
-                if value is not None:
+                if (value is not None) or (self._optcre == self.OPTCRE):
                     key = " = ".join((key, str(value).replace('\n', '\n\t')))
                 fp.write("%s\n" % (key))
             fp.write("\n")
Index: Lib/test/test_cfgparser.py
===================================================================
--- Lib/test/test_cfgparser.py	(revision 84442)
+++ Lib/test/test_cfgparser.py	(working copy)
@@ -530,6 +530,33 @@
     allow_no_value = True
 
 
+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 = StringIO.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):
     def newconfig(self, defaults=None):
         self.cf = self.config_class(defaults=defaults, dict_type=SortedDict)
@@ -563,6 +590,7 @@
         SafeConfigParserTestCase,
         SafeConfigParserTestCaseNoValue,
         SortedTestCase,
+        Issue7005TestCase,
         )