1 files changed, 4 insertions, 4 deletions
diff --git a/stopwatch.py b/stopwatch.py
index cdd405b..516138c 100644
--- a/stopwatch.py
+++ b/stopwatch.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 
 import time
-from typing import Callable
+from typing import Callable, Optional
 
 
 class Timer(object):
@@ -18,8 +18,8 @@ class Timer(object):
     """
 
     def __init__(self) -> None:
-        self.start = None
-        self.end = None
+        self.start = 0.0
+        self.end = 0.0
 
     def __enter__(self) -> Callable[[], float]:
         """Returns a functor that, when called, returns the walltime of the
@@ -29,6 +29,6 @@ class Timer(object):
         self.end = 0.0
         return lambda: self.end - self.start
 
-    def __exit__(self, *args) -> bool:
+    def __exit__(self, *args) -> Optional[bool]:
         self.end = time.perf_counter()
         return None  # don't suppress exceptions