Models with no attributes should just have empty hash fixtures [Sam] (Closes #3563)

railties/lib/rails/generators/test_unit/model/templates/fixtures.yml

@@ -11,9 +11,13 @@ two:
   <%= attribute.name %>: <%= attribute.default %>
 <% end -%>
 <% else -%>
-# one:
-#   column: value
+# This model initially had no columns defined.  If you add columns to the
+# model remove the '{}' from the fixture names and add the columns immediately
+# below each fixture, per the syntax in the comments below
 #
-# two:
-#   column: value
-<% end -%>
+one: {}
+# column: value
+#
+two: {}
+#  column: value
+<% end -%>