MES Move and Complete, How to override default Move Quantity by Null Quantity?

Hello everyone, We are using MES's Move and Complete transaction, but in this transaction option MES suggests by default Move Quantity as same Available Quantity, reviewing in Transaction the original definition is rendered and has a SPEL statement:  "${oa.TransactionPVO1.TxnQtyRequired}" ;   Someone have a suggest on how to change default quantity by NULL?

Thanks