code: @Override
      public Vertex addVertex(Object... keyValues) {
          // check graph is readonly
          if (readonly)
              throw Graph.Exceptions.vertexAdditionsNotSupported();
          // get current session
          Neo4JSession session = currentSession();
          // transaction should be ready for io operations
          transaction.readWrite();
          // add vertex
          return session.addVertex(keyValues);
      }
docs: {@inheritDoc}