Per 4.5.1, the wildcard ? extends Object is equivalent to the unbounded wildcard ?.

In the following example javac emits a different unchecked in one example but not the other, and the only difference is the use of ? vs. ? extends Object.

```
import java.util.List;

class T {
  void f(List<? extends Object> x) {}

  void g(List<?> x) {}

  void h(List<String> x) {
    f((List) x);
    g((List) x);
  }
}
```

$ javac -fullversion -Xlint:all T.java
javac full version "17-ea+24-2164"
T.java:9: warning: [unchecked] unchecked method invocation: method f in class T is applied to given types
    f((List) x);
     ^
  required: List<? extends Object>
  found: List
T.java:9: warning: [unchecked] unchecked conversion
    f((List) x);
      ^
  required: List<? extends Object>
  found: List
2 warnings