Sets cannot be used as property types

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.

boolean
byte
char
short
int
long
float
double
java.lang.Boolean
java.lang.Byte
java.lang.Character
java.lang.Short
java.lang.Integer
java.lang.Long
java.lang.Float
java.lang.Double
java.lang.String
java.util.List
java.util.Map
java.util.Locale