Test if Workbook property exists

I use custom workbook properties to save "settings" for each workbook. Is there a way to test if that property exists?

Here is one Property that I add:

wbWorking.CustomDocumentProperties.Add "Company", False, msoPropertyTypeString, stgCompany

How can I test if that property exists?

And also is there a way to test if Any Custom Properties exist, instead of specific ones?