get_all_properties throws and error

error `AttributeError: 'NoneType' object has no attribute 'startswith'`

```python
import os
from notion.client import NotionClient
token = os.environ.get("NOTION_TOKEN")
PROJECT_COLLECTION = ""

client = NotionClient(token, monitor=False)
collection = client.get_collection(PROJECT_COLLECTION)
projects = collection.get_rows()
project = projects[0]
project.get_all_properties() # <<<<
```

Start at the get_all_properties entry point and reproduce the provided collection-row example to inspect where the NoneType startswith error occurs. Trace the failing property handling and verify that the example completes without raising AttributeError.

Written by the indexing model from the issue text.