No serial number for G10

[vAfotoriporter]

I use a Canon G10 camera as my compact one and it seems not to have a serial number showing up with {snum} variable. I don't know if it is a bug or a feature, but it would help my workflow a lot it it could be handled to PM return a value for it since I put a body identifying letter into my filenames (with code replacements derived from the /{snum}/ variable) but in this case I only get the replacement delimiters and cannot set up the replacement correctly.

Is it possible to at least have an option to replace a given string if a variable doesn't give back any value? If this camera model doesn't allow to get serial number from the image files then say {snum}=nil making it possible to have a codereplacement /{snum}/ be used to put an X (or any other stuff) be used to mark which of my cameras took the picture (or to show it cannot be determined but my filenaming system wouldn't be disrupted by this error.

[vAfotoriporter]

I've been thinking on this issue. Could it be a workaround to make a code replacement having no text to be replaced before the tab just what to be replaced?
I mean:

{tab}replace to this1
replace this2{tab}replace to this2
replace this3{tab}replace to this3

could // result to have replace to this 1 be inserted? This way a variable with no valid result (like {snum} on the G10 could still be used as a valid variable (under certain circumtstances like I don't use any other camera that has no {snum} meaning the only one doesn't have will be this one.
I hope you understand and have any idea.