How can I get the Type from a UnaryExpression?

I have a property defined as Expression<Func<Kitten, object>> which is c => c.KittenAge, where KittenAge is an int?

I want to get the type of this.

My code is:

Expression<Func<Kitten, object>> property = c => c.KittenAge;

var unaryExpression = property.Body as UnaryExpression;

if (Nullable.GetUnderlyingType(unaryExpression.Type) == null)
{
   // Error, must be nullable
}

Unfortunately, the error line is always hit because the Type is System.Object. How can I get the type of int? from the expression?