get_bx wont work with `dict` without 'label' key

**Describe the bug**
get_bx wont work with `dict` without 'label' key

**To Reproduce**
Steps to reproduce the behavior:

```
# passing dict
get_bx({'x_min': 130, 'y_min': 63, 'x_max': 225, 'y_max': 180})
```

**Expected behavior**
Returns a Bx with 'unknown' or empty label.
