code: private <X> X operateOnOpenGraph(Supplier<X> supplier) {
          if (!isLocal() || isClosed()) throw TransactionException.transactionClosed(this, this.closedReason);
          return supplier.get();
      }
docs: An operation on the graph which requires it to be open.
  
  @param supplier The operation to be performed on the graph
  @return The result of the operation on the graph.
  @throws TransactionException if the graph is closed.