import java.util.ArrayList;
import java.util.List;
import org.checkerframework.checker.nullness.qual.NonNull;

class MyTop {
    List<String> children = new ArrayList<>();
}

abstract class PptRelationMin {
    abstract MyTop getPpt();

    void init_hierarchy_new() {
        MyTop ppt = getPpt();

        @NonNull Object o1 = ppt.children;

        for (String rel : ppt.children) ;

        @NonNull Object o2 = ppt.children;
    }
}