Check the value of a device handle data line to see if it has a value or if it is null in LabView

[RichMyers]

I have a case structure inside a while loop with a shift register that holds the value of a device handle. One of the cases is to "Initialize" a device. The other cases cause the device to take some action, or close the device. I want to add some code to the other cases to check the value of the device handle in order to ensure that it is not NULL before I attempt to configure the device. In LabView, how can I check to ensure that the value of the device handle is not null?

[Joe_Guo]

Use the "Not A Number/Path/Refnum?" vi from the "Comparison" palette. But please check the help on this vi before using it. If this does not work for you, then create a ref constant from your vi's input or output.

-Joe