Respond to upstream: use None as type sentinel

Author: dandavison

temporalio/nexus/handler.py

@@ -57,8 +57,8 @@ def _get_workflow_run_start_method_input_and_output_type_annotations(
         Awaitable[WorkflowHandle[Any, O]],
     ],
 ) -> tuple[
-    Union[Type[I], Type[nexusrpc.handler.MISSING_TYPE]],
-    Union[Type[O], Type[nexusrpc.handler.MISSING_TYPE]],
+    Optional[Type[I]],
+    Optional[Type[O]],
 ]:
     """Return operation input and output types.
 
@@ -76,15 +76,15 @@ def _get_workflow_run_start_method_input_and_output_type_annotations(
             f"Expected return type of {start_method.__name__} to be a subclass of WorkflowHandle, "
             f"but is {output_type}"
         )
-        output_type = nexusrpc.handler.MISSING_TYPE
+        output_type = None
 
     args = typing.get_args(output_type)
     if len(args) != 2:
         warnings.warn(
             f"Expected return type of {start_method.__name__} to have exactly two type parameters, "
             f"but has {len(args)}: {args}"
         )
-        output_type = nexusrpc.handler.MISSING_TYPE
+        output_type = None
     else:
         _wf_type, output_type = args
     return input_type, output_type

temporalio/worker/_nexus.py

@@ -371,12 +371,7 @@ async def deserialize(
         try:
             [input] = await self.data_converter.decode(
                 [self.payload],
-                type_hints=(  # type: ignore
-                    [as_type]
-                    # TODO(nexus-prerelease): HACK
-                    if (as_type and as_type != nexusrpc.handler.MISSING_TYPE)
-                    else [Any]
-                ),
+                type_hints=[as_type] if as_type else None,
             )
         except Exception as err:
             raise nexusrpc.handler.HandlerError(