upcast can never yield an unchecked warning

I am tuning the JDT compiler near unchecked cast, and looking back at the
official words from JLS, I noticed that it isn't quite covering all
aspects.
According to the spec, an upcast can never yield an unchecked warning,
though javac emits one for this case:

import java.util.*;
public class X {

      public static class DatabaseObject {}
      public static class ObjectFormUI<T extends DatabaseObject> {}
      private static final Map<Class<? extends DatabaseObject>, Class<?
extends ObjectFormUI>> uiMap = new HashMap<Class<? extends DatabaseObject>,
Class<? extends ObjectFormUI>>();

      public static <T extends DatabaseObject> Class<? extends
ObjectFormUI<T>> getUI(
                  Class<T> persistentClass) {
            return null != null
                  ? uiMap.get(persistentClass)
                  : (Class<? extends ObjectFormUI<T>>)
uiMap.get(persistentClass); // unchecked
      }
}