TypeSrcript ref(null) value cant be assign (Object is possible null)

Why is this error coming out?

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Set default value to null
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Assigned on mounted
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And yet, this code is not yet being called.
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Damn typescript,
My guess this error should not be coming. tsk tsk

Okay, seems like using typescript is not a good choice,
Just got remove the lang="ts" from the <script> tag