LUB is computed incorrectly when involving bounded type variables

class Foo<T> {}
class Main {
  static final <T extends Foo<String>> T test() {
    final T x = null;
    true ? (T) null: x
  }
}

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
test.groovy: 6: [Static type checking] - Cannot return value of type Foo<java.lang.Object> on method returning type T
 @ line 6, column 5.
       true ? (T) null: x
       ^1 error