Return None type instead of exception

flytekit/core/promise.py

@@ -570,10 +570,10 @@
         )
 
     elif isinstance(t_value, list):
-        sub_type: type = ListTransformer.get_sub_type(t_value_type)
+        sub_type: Optional[type] = ListTransformer.get_sub_type_or_none(t_value_type)
         collection = _literals_models.BindingDataCollection(
             bindings=[
-                binding_data_from_python_std(ctx, expected_literal_type.collection_type, t, sub_type, nodes)
+                binding_data_from_python_std(ctx, expected_literal_type.collection_type, t, sub_type or type(t), nodes)
                 for t in t_value
             ]
         )

flytekit/core/type_engine.py

@@ -1108,6 +1108,16 @@
         """
         Return the generic Type T of the List
         """
+        if (sub_type := ListTransformer.get_sub_type_or_none(t)) is not None:
+            return sub_type
+
+        raise ValueError("Only generic univariate typing.List[T] type is supported.")
+
+    @staticmethod
+    def get_sub_type_or_none(t: Type[T]) -> Optional[Type[T]]:
+        """
+        Return the generic Type T of the List, or None if the generic type cannot be inferred
+        """
         if hasattr(t, "__origin__"):
             # Handle annotation on list generic, eg:
             # Annotated[typing.List[int], 'foo']
@@ -1117,7 +1127,7 @@
             if getattr(t, "__origin__") is list and hasattr(t, "__args__"):
                 return getattr(t, "__args__")[0]
 
-        raise ValueError("Only generic univariate typing.List[T] type is supported.")
+        return None
 
     def get_literal_type(self, t: Type[T]) -> Optional[LiteralType]:
         """

tests/flytekit/unit/core/test_type_engine.py

@@ -2334,3 +2334,11 @@ class Datum(DataClassJSONMixin):
     pv = transformer.to_python_value(ctx, lv, expected_python_type=gt)
     assert datum_mashumaro.x == pv.x
     assert datum_mashumaro.y.value == pv.y
+
+
+def test_ListTransformer_get_sub_type():
+    assert ListTransformer.get_sub_type_or_none(typing.List[str]) is str
+
+
+def test_ListTransformer_get_sub_type_as_none():
+    assert ListTransformer.get_sub_type_or_none(type([])) is None