@Override
  public void addOutEdge(E edge, N node) {
    super.addOutEdge(edge, node);
    Multiset<N> adjacentNodes = getReference(adjacentNodesReference);
    if (adjacentNodes != null) {
      checkState(adjacentNodes.add(node));
    }
  }

  private static <T> @Nullable T getReference(@Nullable Reference<T> reference) {
    return (reference == null) ? null : reference.get();
  }

    N node = super.removeInEdge(edge, isSelfLoop);
    Multiset<N> predecessors = getReference(predecessorsReference);
    if (predecessors != null) {
      checkState(predecessors.remove(node));
    }
    return node;
  }

  @Override
  public N removeOutEdge(E edge) {
    N node = super.removeOutEdge(edge);
    Multiset<N> successors = getReference(successorsReference);
    if (successors != null) {

    N node = super.removeInEdge(edge, isSelfLoop);
    Multiset<N> predecessors = getReference(predecessorsReference);
    if (predecessors != null) {
      checkState(predecessors.remove(node));
    }
    return node;
  }

  @Override
  public N removeOutEdge(E edge) {
    N node = super.removeOutEdge(edge);
    Multiset<N> successors = getReference(successorsReference);
    if (successors != null) {

## Other notable changes

### API Machinery

- Remove `GetReference()` and `GetPartialReference()` function from `pkg/api/ref`, as the same function exists also in `staging/src/k8s.io/client-go/tools/ref` ([#80361](https://github.com/kubernetes/kubernetes/pull/80361), [@wojtek-t](https://github.com/wojtek-t))