mypy: Fix implicit optional usage

Current versions of mypy run with no-implicit-optional
by default.  This change gets Nova's mypy test environment
to pass again.

Change-Id: Ie50c8d364ad9c339355cc138b560ec4df14fe307

1 files changed, 6 insertions, 1 deletions

diff --git a/nova/virt/libvirt/event.py b/nova/virt/libvirt/event.py
index a7d2a3624f..56951dc11c 100644
--- a/nova/virt/libvirt/event.py
+++ b/nova/virt/libvirt/event.py
@@ -9,6 +9,8 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
+import typing as ty
+
 from nova.virt import event
 
 
@@ -22,7 +24,10 @@ class LibvirtEvent(event.InstanceEvent):
 class DeviceEvent(LibvirtEvent):
     """Base class for device related libvirt events"""
 
-    def __init__(self, uuid: str, dev: str, timestamp: float = None):
+    def __init__(self,
+                 uuid: str,
+                 dev: str,
+                 timestamp: ty.Optional[float] = None):
         super().__init__(uuid, timestamp)
         self.dev = dev