Bindings.inputValue returns null in page composer

Summary: Hi, I am trying to make a field mandatory based on another field value through Page Composer.

But when I test Bindings.inputValue returns null, all fields having same issue.

#{bindings.InvoiceTypeLookupCode.inputValue =='M1' ? true: false}

For above syntax when I click test it should show true, because I gave value of InvoiceTypeLookupCode as M1. But shows false.
If I use like below and click test it works fine.
#{3+4 =='7' ? true: false}. So that means bindings.InvoiceTypeLookupCode.inputValue returns nothing

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