KeyError: 'facets'

Sometimes I get a key error on `facets`, I could not reproduce it. I am wondering if this is something normal and if you know in what condition it could happen ?

```python
results = index.search("", {"facets": "*"})
facets = results['facets'] # <== sometimes the key is not present
```

从 `index.search("", {"facets": "*"})` 示例开始，检查 Python 客户端如何构建和返回搜索结果。如果可能，复现缺失的 `facets` 键，然后确定并记录能够解释这一现象的条件或行为；如果 repository 提供了适当的回归检查，则添加该检查。

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