Add Missing None return type in Vesync

[cdnninja]

Proposed change

Return type cleanup to reduce size of #160573

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[home-assistant]

Hey there @markperdue, @webdjoe, @TheGardenMonkey, @iprak, @SapuSeven, mind taking a look at this pull request as it has been labeled with an integration (vesync) you are listed as a code owner for? Thanks!

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[zweckj]

what does it mean if those two return None? Should the entity be unavailable instead?

[TheJulianJES]

This seems fine? Returning None should cause the entity to assume unknown state, becoming greyed out in the frontend, similar as to when it’s unavailable.

The typing in the base Humidifier class already allows for this, see here.

[zweckj]

This seems fine?

Technically yes. We were just returning unknown too often in the past, instead of making the entity unavailable, that's why I'm usually asking when we are returning None

[cdnninja]

This was done for mypy reasons. The variable the library starts as None until first API call. After that I wouldn't expect it to be None. If an update fails the device will go unavailable.

[zweckj]

then usually we tend to add

if TYPE_CHECKING:
    assert ...

so it's clear it won't return unkown

[cdnninja]

Thank you! I love learning these tricks. Appreciated. Ready for review with the above included.