Check if a custom property is empty

I want to do a macro that will save as a 3D model with a different name but only only if some custom properties with a specific name are not empty. I'm a beginner with SolidWorks's macro, I know how to save as my part with a different name, but i don't know how to check if a custom property is empty or not. Can someone help me with that ?

Thanks

SolidworksApi macros