Incompatible return type when returning empty list and annotation is Union[List]

[matteosantama]

def fn1(data: list[int]) -> list[int]:
    return []


def fn2(data: list[int]) -> list[int] | list[str]:
    return []

mypy has no problem with the first function, but complains about the other.

error: Incompatible return value type (got "List[<nothing>]", expected "Union[List[int], List[str]]")  [return-value]

• Mypy version used: mypy 0.971 (compiled: yes)
• Python version used: Python 3.10.4
• Operating system and version: macOS Monterey 12.4