doc error in jdk.internal.module.Resources.toPackageName(String)

A DESCRIPTION OF THE PROBLEM :
The javadoc of jdk.internal.module.Resources.toPackageName(String) does not match its implementation:
> This method returns null if the resource name ends with a "/"

Implementation:
```
int index = name.lastIndexOf('/');
if (index == -1 || index == name.length()-1) {
    return "";
}
```

See https://github.com/openjdk/jdk/blob/b6d51e15549e11be583625d908192d9f7f049489/src/java.base/share/classes/jdk/internal/module/Resources.java#L62

Maybe it would be saner to follow the documentation comment and return `null` instead of an empty String, otherwise this could accidentally or maliciously cause unwanted behavior.