BugInCF type is not an erased subtype of supertype about checker-framework HOT 1 OPEN

package typearginfer;

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Collectors;

public class Issue6762 {

  void method(ResultSet rs) throws SQLException {
    final IntSet roleIds = Optional.ofNullable(rs.getString("role_ids")).map(
            rids -> Arrays.stream(rids.split(",")).map(Integer::parseInt)
                .collect(Collectors.collectingAndThen(Collectors.toSet(), IntArraySet::new)))
        .orElse(new IntArraySet());
  }

  static class IntArraySet extends IntSet {
    IntArraySet() {}
    IntArraySet(Set<Integer> i) {}
  }

  static class IntSet implements Set<Integer> {


    @Override
    public int size() {
      return 0;
    }

    @Override
    public boolean isEmpty() {
      return false;
    }

    @Override
    public boolean contains(Object o) {
      return false;
    }

    @Override
    public Iterator<Integer> iterator() {
      return null;
    }

    @Override
    public Object[] toArray() {
      return new Object[0];
    }

    @Override
    public <T> T[] toArray(T[] a) {
      return null;
    }

    @Override
    public boolean add(Integer integer) {
      return false;
    }

    @Override
    public boolean remove(Object o) {
      return false;
    }

    @Override
    public boolean containsAll(Collection<?> c) {
      return false;
    }

    @Override
    public boolean addAll(Collection<? extends Integer> c) {
      return false;
    }

    @Override
    public boolean retainAll(Collection<?> c) {
      return false;
    }

    @Override
    public boolean removeAll(Collection<?> c) {
      return false;
    }

    @Override
    public void clear() {}
  }
}