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

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

    }

    public Throwable getException() {
        return exception;
    }

    public String getMessage() {
        return message;
    }

    public String getReference() {
        return reference;
    }

    public List<ExceptionSummary> getChildren() {
        return children;
    }