I create a JavaBean with a Set property because I wanted to enforce that there were only unique values in that Set. However when I tried to use this JavaBean with a properties file, Nucleus complained it could not resolve the elements of the Set property. When I changed the property to be a List or a String  Nucleus had no problem.
Here is the properties file.
$class=com.betweengo.droplet.VerifyImages $scope=request # supported image dimensions supportedImageDimensions=75x90,88x31,120x90
ATG Support pointed me to the Property Types subsection of the Using Nucleus
section of the ATG Programming Guide. Specifically only these simple types are supported. I am not sure why Set was excluded.