@Nonnull
 @ReturnsMutableCopy
 public Set<String> getAllRelatedNodeIDs() {
   final Set<String> ret = new LinkedHashSet<String>();
   if (m_aIncoming != null)
     for (final IDirectedGraphRelation aRelation : m_aIncoming.values())
       ret.add(aRelation.getFromID());
   if (m_aOutgoing != null)
     for (final IDirectedGraphRelation aRelation : m_aOutgoing.values())
       ret.add(aRelation.getToID());
   return ret;
 }