got further

Signed-off-by: Jess Frazelle <github@jessfraz.com>

kittycad/models/mass.py

@@ -41,8 +41,10 @@ class Mass:
         output_unit: Union[Unset, UnitMass]
         if isinstance(_output_unit, Unset):
             output_unit = UNSET
+        if _output_unit is None:
+            output_unit = UNSET
         else:
-            output_unit = _output_unit  # type: ignore[arg-type]
+            output_unit = _output_unit
 
         mass = cls(
             mass=mass,