#5573 [BUG] Flyte seems to fail to deserialize serialized `None` to `NoneType` when this type is eligible. Issue created by JackUrb Hi Flyte Team! I'm running into a strange serialization/deserialization bug around

None

and can't really tease out what exactly causes it. I have a possible fix below, but don't understand enough about the cause to ensure correctness. The basic reproduction involves having one

@task

output a nullable value, and then later using that nullable value as input to another

@task

or

@workflow

. If the value is

None

, it fails to deserialize with the following error:

TypeError: Failed to convert inputs of task 'simple_none_repro.wrap_outer_outputs':
  Failed argument 'output': Python value cannot be None, expected <class 'NoneType'>/[Flyte Serialized object: Type: <LiteralType> 
Value: <simple: NONE>]

Here's a simple repro file: # simple_none_repro.py from flytekit import task, workflow from dataclasses import dataclass from mashumaro.mixins.json import DataClassJSONMixin @dataclass class OuterWorkflowInput(DataClassJSONMixin): input: float @dataclass class OuterWorkflowOutput(DataClassJSONMixin): nullable_output: float | None = None @dataclass class InnerWorkflowInput(DataClassJSONMixin): input: float @dataclass class InnerWorkflowOutput(DataClassJSONMixin): nullable_output: float | None = None @task def inner_task(input: float) -> float | None: if input == 0: return None return input @task def wrap_inner_inputs(input: float) -> InnerWorkflowInput: return InnerWorkflowInput(input=input) @task def wrap_inner_outputs(output: float | None) -> InnerWorkflowOutput: return InnerWorkflowOutput(nullable_output=output) @task def wrap_outer_outputs(output: float | None) -> OuterWorkflowOutput: return OuterWorkflowOutput(nullable_output=output) @workflow def inner_workflow(input: InnerWorkflowInput) -> InnerWorkflowOutput: return wrap_inner_outputs( output=inner_task( input=input.input ) ) @workflow def outer_workflow(input: OuterWorkflowInput) -> OuterWorkflowOutput: inner_outputs = inner_workflow( input=wrap_inner_inputs(input=input.input) ) return wrap_outer_outputs( output=inner_outputs.nullable_output ) if name == "__main__": print(outer_workflow(OuterWorkflowInput(input=1))) # works fine print(outer_workflow(OuterWorkflowInput(input=0))) # fails with the above error I've been able to "resolve" the issue in a local patch to

flytekit

that makes the following change to this line: if (python_val is None and python_type != NoneType) and expected and expected.union_type is None: Doing this makes the above file run cleanly:

>> python simple_none_repro.py
OuterWorkflowOutput(nullable_output=1.0)
OuterWorkflowOutput(nullable_output=None)

flyteorg/flyte