Review comment.

src/zope/i18nmessageid/message.py

@@ -36,15 +36,16 @@ def __new__(cls, ustr, domain=None, default=None, mapping=None,
                 msgid_plural=None, default_plural=None, number=None):
         self = six.text_type.__new__(cls, ustr)
         if isinstance(ustr, self.__class__):
-            domain = ustr.domain and ustr.domain[:] or domain
-            default = ustr.default and ustr.default[:] or default
-            mapping = ustr.mapping and ustr.mapping.copy() or mapping
+            domain = domain if ustr.domain is None else ustr.domain[:]
+            default = default if ustr.default is None else ustr.default[:]
+            mapping = mapping if ustr.mapping is None else ustr.mapping.copy()
             msgid_plural = (
-                ustr.msgid_plural and ustr.msgid_plural[:] or msgid_plural)
+                msgid_plural if ustr.msgid_plural is None else
+                ustr.msgid_plural[:])
             default_plural = (
-                ustr.default_plural and ustr.default_plural[:]
-                or default_plural)
-            number = ustr.number is not None and ustr.number or number
+                default_plural if ustr.default_plural is None else
+                ustr.default_plural[:])
+            number = number if ustr.number is None else ustr.number
             ustr = six.text_type(ustr)
 
         self.domain = domain
@@ -55,7 +56,6 @@ def __new__(cls, ustr, domain=None, default=None, mapping=None,
 
         if number is not None and not isinstance(
                 number, six.integer_types + (float,)):
-            # Number must be an integer
             raise TypeError('`number` should be an integer or a float')
 
         self.number = number

src/zope/i18nmessageid/tests.py

@@ -70,6 +70,21 @@ def test_values_with_float_for_number(self):
         if self._TEST_READONLY:
             self.assertTrue(message._readonly)
 
+    def test_values_with_zero(self):
+        mapping = {'key': 'value'}
+        message = self._makeOne(
+            'testing', 'domain', 'default', mapping,
+            msgid_plural='testings', default_plural="defaults", number=0)
+        self.assertEqual(message, 'testing')
+        self.assertEqual(message.domain, 'domain')
+        self.assertEqual(message.default, 'default')
+        self.assertEqual(message.mapping, mapping)
+        self.assertEqual(message.msgid_plural, 'testings')
+        self.assertEqual(message.default_plural, 'defaults')
+        self.assertEqual(message.number, 0)
+        if self._TEST_READONLY:
+            self.assertTrue(message._readonly)
+
     def test_copy(self):
         mapping = {'key': 'value'}
         source = self._makeOne(