Is that any way to tell if the terminal is connected or not?

Hi all,

  I am designing a subvi to accept 4 inputs. 3 of them are DBL and the last one is boolean. the boolean input could be connected or not. If it does not feed with external value, then it will use those 3 DBL values to do the calculation but if it is feed by either true or false, a special value will be used for calculation. Now the question is how can I tell if that terminal is connected or not?