[Bug]: 添加第二个节点出现 TypeError: Cannot read properties of null (reading '0')

### Describe the bug / 问题描述

当使用 graph.addNodeData([newNode]); 空白画布添加第一个节点没问题，添加第二个节点出现 TypeError: Cannot read properties of null (reading '0')

### Reproduction link / 复现链接

_No response_

### Steps to Reproduce the Bug or Issue / 重现步骤

_No response_

### Version / 版本

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### OS / 操作系统

- [ ] macOS
- [ ] Windows
- [ ] Linux
- [ ] Others / 其他

### Browser / 浏览器

- [ ] Chrome
- [ ] Edge
- [ ] Firefox
- [ ] Safari (Limited support / 有限支持)
- [ ] IE (Nonsupport / 不支持)
- [ ] Others / 其他

Start by reproducing the failure with graph.addNodeData([newNode]) on a blank canvas, adding one node and then a second. Trace the resulting TypeError and verify that adding the second node completes without reading from null; the issue provides no reproduction link, version, or named test.

Written by the indexing model from the issue text.