Fix router create/show if extraroute not supported

If neutron does not support extraroute l3 extension, the route column
formatter fails.

Change-Id: I7b89c4f818865073947e0850e86c18d0d2415a51

Author: Édouard Thuleau

openstackclient/network/v2/router.py

@@ -49,7 +49,7 @@ def human_readable(self):
 class RoutesColumn(cliff_columns.FormattableColumn):
     def human_readable(self):
         # Map the route keys to match --route option.
-        for route in self._value:
+        for route in self._value or []:
             if 'nexthop' in route:
                 route['gateway'] = route.pop('nexthop')
         return utils.format_list_of_dicts(self._value)

openstackclient/tests/unit/network/v2/test_router.py

@@ -1285,6 +1285,24 @@ def test_show_no_ha_no_distributed(self):
         self.assertNotIn("is_distributed", columns)
         self.assertNotIn("is_ha", columns)
 
+    def test_show_no_extra_route_extension(self):
+        _router = network_fakes.FakeRouter.create_one_router({'routes': None})
+
+        arglist = [
+            _router.name,
+        ]
+        verifylist = [
+            ('router', _router.name),
+        ]
+        parsed_args = self.check_parser(self.cmd, arglist, verifylist)
+
+        with mock.patch.object(
+                self.network, "find_router", return_value=_router):
+            columns, data = self.cmd.take_action(parsed_args)
+
+        self.assertIn("routes", columns)
+        self.assertIsNone(list(data)[columns.index('routes')].human_readable())
+
 
 class TestUnsetRouter(TestRouter):