Serialize a dict with non-orderable keys

It seems that it is not possible to serialize a dict which a non-orderable keys:

```python
from ipykernel.serialize import serialize_object
serialize_object({'A': 1, 2: 2})

File "...\ipykernel\serialize.py", line 85, in serialize_object
for k in sorted(obj):
TypeError: '<' not supported between instances of 'int' and 'str'
```
Is ordering the keys mandatory to serialize the dict? (sorry if that is a dumb question)