Add overloaded annotations of epoch_to_datetime to fs.time

Author: althonos

fs/time.py

@@ -4,10 +4,14 @@
 from __future__ import print_function
 from __future__ import unicode_literals
 
+import typing
 from calendar import timegm
 from datetime import datetime
 from pytz import UTC, timezone
 
+if typing.TYPE_CHECKING:
+    from typing import Optional
+
 
 utcfromtimestamp = datetime.utcfromtimestamp
 utclocalize = UTC.localize
@@ -20,7 +24,19 @@ def datetime_to_epoch(d):
     return timegm(d.utctimetuple())
 
 
-def epoch_to_datetime(t):
+@typing.overload
+def epoch_to_datetime(t):  # noqa: D103
+    # type: (None) -> None
+    pass
+
+
+@typing.overload
+def epoch_to_datetime(t):  # noqa: D103
     # type: (int) -> datetime
+    pass
+
+
+def epoch_to_datetime(t):
+    # type: (Optional[int]) -> Optional[datetime]
     """Convert epoch time to a UTC datetime."""
     return utclocalize(utcfromtimestamp(t)) if t is not None else None