Checking if a Custom Property Exists

[Matt Denton]

Hello all,

Does anyone know how to check if a custom property exists?

I've tried:

put exists (the gCustomProp of this stack)

and:

put there is a (the gCustomProp of this stack)

... both yielding 'false' for a property that does exist and holds a 
value. Short of cycling through the prop list, I can't work out any 
other way.

Many thanks!

Matt Denton