Why does PyCheck complain about assigning T to Optional[T]?

[xorcus]

I am calling a function that accepts Optional[T], meaning it accepts T and knows how to handle None, i.e. T | None.
I like PyCheck's strict type checking because I want my code to adhere to a high quality standard, except for PyCheck complaining when I want to supply T I know is never None to a function accepting T | None. Even for strict type checking, this complaint seems plain wrong to me. Could you please provide the justification why PyCheck believes I should not be allowed to assign T to T|None?

[xorcus]

Turns out my problem came from another issue. The import of T (SecretStr in my case) became invalid as the type moved to another package. Originally it was:

from pydantic import SecretStr

And it had to be changed to:

from langchain_core.pydantic_v1 import SecretStr

In the end, it was a mismatch between two different SecretStr types.