docs: protected Edge buildConcrete11Edge(Vertex vertex1, Vertex vertex2, boolean fkToRef)
      {
          ModificationState state1 = vertex1.getEnvelope().getModificationState();
          ModificationState state2 = vertex2.getEnvelope().getModificationState();
          if (state1.needsUpdate() || state1.needsInsert())
          {
              if (state2.needsInsert())
              {
                  // (2) must be inserted before (1) can point to it
                  return new Edge(vertex2, vertex1, fkToRef ? CONCRETE_EDGE_WEIGHT_WITH_FK : CONCRETE_EDGE_WEIGHT);
              }
          }
          else if (state1.needsDelete())
          {
              if (state2.needsDelete())
              {
                  // (1) points to (2) and must be deleted first 
                  return new Edge(vertex1, vertex2, fkToRef ? CONCRETE_EDGE_WEIGHT_WITH_FK : CONCRETE_EDGE_WEIGHT);
              }
          }
          return null;
      }