fix: uiManager can be nil

[hirbod]

I talked with Tomasz from Expo and he said that uiManager can be nil too, so it was fine in the first place.

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[lodev09]

Not sure if ? will help though... it could still crash if this becomes nil?

[lodev09]

I'd say we stick to the type provided by RN. if it crashes, then there's definitely something else going on and might help dev to debug.