diff --git a/swh/model/model.py b/swh/model/model.py
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -96,6 +96,9 @@
     if type_ is object or type_ is Any:
         return True
 
+    if type_ is None:
+        return value is None
+
     origin = getattr(type_, "__origin__", None)
 
     # Non-generic type, check it directly
diff --git a/swh/model/tests/test_model.py b/swh/model/tests/test_model.py
--- a/swh/model/tests/test_model.py
+++ b/swh/model/tests/test_model.py
@@ -137,6 +137,7 @@
         [None, bytearray(b"\x12\x34"), "123", 0, 123, (), (1, 2, 3), ImmutableDict()],
     ),
     (str, ["", "123"], [None, b"123", b"", 0, (), (1, 2, 3), ImmutableDict()]),
+    (None, [None], [b"", b"123", "", "foo", 0, 123, ImmutableDict(), float("NaN")]),
     # unions:
     (
         Optional[int],