How to clear the date field with checkbox when unchecked ?

Hi Expert

I have some problem to set date field be empty.

This's my code,

If(myCheckBox == False)

{

  SalesParam.TransDate.valueStr() == datenull();

}

Or

If(myCheckBox == False)

{

  SalesParam.TransDate = datenull();

}

I have try this code but still error,?

Can someone share. What should i do ?