Impossible to save resource with update_fields with empty list values

Currently it fails if I explicitly want to set some attributes to empty list using patch 
It's regression in 2.0.6, because it started to remove null and empty values
```
resource = client.resource("Patient", generalPractitioner=[practitioner1])
await resource.save()

resource["generalPractitioner"] = []
await resource.save(update_fields=["generalPractitioner"])
```