docs: protected Edge buildPotential11Edge(Vertex vertex1, Vertex vertex2, boolean fkToRef)
      {
          ModificationState state1 = vertex1.getEnvelope().getModificationState();
          ModificationState state2 = vertex2.getEnvelope().getModificationState();
          if (state1.needsUpdate() || state1.needsDelete())
          {
              if (state2.needsDelete())
              {
                  // old version of (1) might point to (2)
                  return new Edge(vertex1, vertex2, fkToRef ? POTENTIAL_EDGE_WEIGHT_WITH_FK : POTENTIAL_EDGE_WEIGHT);
              }
          }
          return null;
      }