`dandiset.get_metadata` not working for some dandisets

```python
from dandi.dandiapi import DandiAPIClient

client = DandiAPIClient()
dandisets = list(client.get_dandisets())

# this works
dandisets[-3].get_metadata()

# this does not work
for dandiset in dandisets:
metadata = dandiset.get_metadata()
```

```pytb
---------------------------------------------------------------------------
ValidationError Traceback (most recent call last)
Cell In[13], line 12
10 # this does not work
11 for dandiset in tqdm(dandisets):
---> 12 metadata = dandiset.get_metadata()

File /opt/conda/lib/python3.10/site-packages/dandi/dandiapi.py:925, in RemoteDandiset.get_metadata(self)
920 def get_metadata(self) -> models.Dandiset:
921 """
922 Fetch the metadata for this version of the Dandiset as a
923 `dandischema.models.Dandiset` instance
924 """
--> 925 return models.Dandiset.parse_obj(self.get_raw_metadata())

File /opt/conda/lib/python3.10/site-packages/pydantic/main.py:527, in pydantic.main.BaseModel.parse_obj()

File /opt/conda/lib/python3.10/site-packages/pydantic/main.py:342, in pydantic.main.BaseModel.__init__()

ValidationError: 1 validation error for Dandiset
license
ensure this value has at least 1 items (type=value_error.list.min_items; limit_value=1)
```