False evaluating values are now serialized to colander.null for String, Date, and Time

colander/__init__.py

@@ -901,7 +901,7 @@ class String(SchemaType):
         self.encoding = encoding
 
     def serialize(self, node, appstruct):
-        if appstruct is null:
+        if not appstruct:
             return null
 
         try:
@@ -1307,7 +1307,7 @@ class Date(SchemaType):
     err_template =  _('Invalid date')
 
     def serialize(self, node, appstruct):
-        if appstruct is null:
+        if not appstruct:
             return null
 
         if isinstance(appstruct, datetime.datetime):
@@ -1383,7 +1383,7 @@ class Time(SchemaType):
     err_template =  _('Invalid time')
 
     def serialize(self, node, appstruct):
-        if appstruct is null:
+        if not appstruct:
             return null
 
         if isinstance(appstruct, datetime.datetime):

colander/tests/test_colander.py

@@ -1078,6 +1078,14 @@ class TestString(unittest.TestCase):
         result = typ.serialize(node, null)
         self.assertEqual(result, null)
 
+    def test_serialize_none(self):
+        import colander
+        val = None
+        node = DummySchemaNode(None)
+        typ = self._makeOne()
+        result = typ.serialize(node, val)
+        self.assertEqual(result, colander.null)
+
     def test_serialize_uncooperative(self):
         val = Uncooperative()
         node = DummySchemaNode(None)
@@ -1677,6 +1685,14 @@ class TestDate(unittest.TestCase):
         result = typ.serialize(node, val)
         self.assertEqual(result, colander.null)
 
+    def test_serialize_none(self):
+        import colander
+        val = None
+        node = DummySchemaNode(None)
+        typ = self._makeOne()
+        result = typ.serialize(node, val)
+        self.assertEqual(result, colander.null)
+
     def test_serialize_with_garbage(self):
         typ = self._makeOne()
         node = DummySchemaNode(None)
@@ -1762,6 +1778,14 @@ class TestTime(unittest.TestCase):
         result = typ.serialize(node, val)
         self.assertEqual(result, colander.null)
 
+    def test_serialize_none(self):
+        import colander
+        val = None
+        node = DummySchemaNode(None)
+        typ = self._makeOne()
+        result = typ.serialize(node, val)
+        self.assertEqual(result, colander.null)
+
     def test_serialize_with_garbage(self):
         typ = self._makeOne()
         node = DummySchemaNode(None)