EL Expression for PO Number field check returns Null everytime

Summary:

I'm creating this EL Expression to make one or two of the fields Mandatory only if the PO Number field is null, on the Create Invoices (Payables) page.

#{empty bindings.PoHeader1.inputValue ? true : false}

But even when the PO Number field has a value, this is evaluating to true in the Test (that is, even when the PO Number is NOT NULL, expression is giving considering it as Null).

Can someone kindly suggest some solution, or an alternate EL expression that may help…!?

Thanks in advance!!!

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