[BUG] Bug handling Optional type hints under conditionals.

[dansola]

Describe the bug

The type engine cannot parse Optional types when dealing with conditionals using variables coming from dynamic workflows.

The scalar.primitive.string_value in the example is embedded in a scalar.union.value and cannot be found.

Expected behavior

The type engine can handle the Optional type under most circumstances, but it should not throw an error in the following example with a dynamic workflow and conditional.

Additional context to reproduce

1. Run this workflow with pyflyte --verbose run workflows/optional_wf_2.py optional_wf

from typing import Optional, Tuple

from flytekit import dynamic, conditional, task
from flytekit import workflow


@dynamic
def get_str(i: int) -> Tuple[int, Optional[str]]:
    my_str = None
    if i > 0:
        my_str = "test"
    return i + 2, my_str


@task
def return_something(my_str: str) -> str:
    return my_str


@task
def dont_return_something() -> Optional[str]:
    return None


@workflow
def optional_wf():
    i = 1
    j, my_str = get_str(i=i)
    (
        conditional("check_str")
        .if_(j > 0)
        .then(return_something(my_str=my_str))
        .else_()
        .then(dont_return_something())
    )


if __name__ == "__main__":
    optional_wf()

2. Observe the following error:

Traceback (most recent call last) 
/lib/python3.11/site-packages/flytekit/core/type_engine.py:250 in to_python_value
❱  250 res = self._from_literal_transformer(lv) 
/lib/python3.11/site-packages/flytekit/core/type_engine.py:1970 in <lambda>                                                                                                                                                                                                                                                                                                                                                  
❱ 1970 lambda x: x.scalar.primitive.string_value,                                                                                                                                           
AttributeError: 'NoneType' object has no attribute 'string_value'

Screenshots

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• [X] Yes

Have you read the Code of Conduct?

• [X] Yes