[Bug] globalNamespaceID specified, but not generated in the toc data of _site/api/index.html

**Version**
docfx-win-x64-v2.71.1(May also apply to other version)

**Describe the bug**
Specify the following metadata settings:

```
"globalNamespaceId": "Global"
"dest": "api"
```

In the api directory, classed in global namespace generated correct yaml in "Global." prefix.
But when I browse the result site, the TOC shows no "Global" tree node. If I type any class name in global namespace into the TOC filter text box, a tree node with no name will be displayed as the parent node of my filtered class.

Look into the html output files in directory "_site", the The name attribute and the display text of this node is empty in "api/index,html" and "api/toc,html". And for the toc.json, it shows null for its name.