hdf5 provider does not support string

This is due to this following HDF5 file

backend = "foo"
h5["/ending/options/backend"] = backend

et
  File "src/gevent/event.py", line 359, in gevent._gevent_cevent.AsyncResult.get
  File "src/gevent/event.py", line 347, in gevent._gevent_cevent.AsyncResult.get
  File "src/gevent/event.py", line 327, in gevent._gevent_cevent.AsyncResult._raise_exception
  File "/nobackup/lvalls1/valls/Software/miniconda3/envs/tomodemo-daiquiri-env/lib/python3.7/site-packages/gevent/_compat.py", line 65, in reraise
    raise value.with_traceback(tb)
  File "/nobackup/lvalls1/valls/Software/miniconda3/envs/tomodemo-daiquiri-env/lib/python3.7/site-packages/gevent/threadpool.py", line 167, in __run_task
    thread_result.set(func(*args, **kwargs))
  File "/users/valls/workspace/daiquiri-tomo.git/daiquiri.git/daiquiri/core/components/hdf5.py", line 66, in gzip
    return gzipped(group)
  File "/users/valls/workspace/daiquiri-tomo.git/daiquiri.git/daiquiri/core/responses.py", line 204, in gzipped
    data_to_bytes = json.dumps(data).encode("utf-8")
  File "/nobackup/lvalls1/valls/Software/miniconda3/envs/tomodemo-daiquiri-env/lib/python3.7/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "/nobackup/lvalls1/valls/Software/miniconda3/envs/tomodemo-daiquiri-env/lib/python3.7/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/nobackup/lvalls1/valls/Software/miniconda3/envs/tomodemo-daiquiri-env/lib/python3.7/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/nobackup/lvalls1/valls/Software/miniconda3/envs/tomodemo-daiquiri-env/lib/python3.7/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type bytes_ is not JSON serializable