Concurrent Program Null Bind Variable

Hi,

I would like to ask for help about the bind variable. When we use the bind variable parameter, the value on parameter2 will be dependend on the value of parameter1 and the parameter2 will be disabled unless there is a value for parameter1.  But is there a way to make the still get the value of paramater two when the parameter1 is null or the user want to enter only the parameter two?

Thanks