Unknown Format Code 'x' on InterfaceLUID

[MarkBaggett]

When an InterfaceLUID in the Network Data Usage Table is blank in the SRUM Database it will generate the following error:

Traceback (most recent call last):
File "srum_dump.py", line 293, in d
ValueError: Unknown format code 'x' for object of type 'str'

This is the result of improper handling of empty values and likely affects other fields as well.

Thanks to @gpriewe and @GregoryDC for helping me track this one down.