built in emulator errors with `multipart/form-data`

When attempting to send it multipart form data to the local emulator, I've encountered this issue:
```json
{'errorMessage': 'Unable to unmarshal input: Expecting value: line 1 column 2 (char 1)', 'errorType': 'Runtime.UnmarshalError', 'requestId': '9aca3c44-1abd-459b-9343-3c32ba2a8ffe', 'stackTrace': []}
```

The code i am running to call my handler:
```python
files = [("file", ("file1.txt", open("/dir/file1.txt")))]
response = requests.post(
f"http://localhost:9000/2015-03-31/functions/function/invocations",
files=files
)
```

Is this supposed to happen? Is there any work to support this right now?