[BUG] Handle Optional FlyteFile in dataclasses

[eapolinario]

Describe the bug

The dataclass type transformer does not handle fields of type Optional[FlyteFile] correctly.

For example, this workflow fails:

from dataclasses import dataclass
from typing import Optional

from dataclasses_json import dataclass_json
from flytekit import workflow, task
from flytekit.types.file import FlyteFile


@dataclass_json
@dataclass
class TaskOutput:
    file1: FlyteFile
    file2: Optional[FlyteFile]

@task
def task1() -> TaskOutput:
    with open("file21.txt", "w+") as f:
        f.write("b")
    with open("file22.txt", "w+") as f:
        f.write("c")

    return TaskOutput(
        FlyteFile("file21.txt", remote_path="s3://my-s3-bucket/tmp/file21.txt"),
        FlyteFile("file22.txt", remote_path="s3://my-s3-bucket/tmp/file22.txt")
    )

@task
def assert_values_in_dataclass(to: TaskOutput):
    assert to.file1.remote_source == "s3://my-s3-bucket/tmp/file21.txt"
    assert to.file2.remote_source == "s3://my-s3-bucket/tmp/file22.txt"


@workflow
def wf():
    to = task1()
    assert_values_in_dataclass(to=to)

Expected behavior

Optional[FlyteFile] should be allowed in Dataclasses.

Additional context to reproduce

No response

Screenshots

No response

Are you sure this issue hasn't been raised already?

• Yes

Have you read the Code of Conduct?

• Yes