SerializationWarning and RuntimeWarning when Combining Echodata Objects

[ctuguinay]

When I was working on the Krill Notebook in Echopype-Examples, I got the two warnings:

/home/exouser/miniforge3/envs/echopype/lib/python3.9/site-packages/xarray/core/dataset.py:2548: SerializationWarning: saving variable None with floating point data as an integer dtype without any _FillValue to use for NaNs
  return to_zarr(  # type: ignore[call-overload,misc]
/home/exouser/miniforge3/envs/echopype/lib/python3.9/site-packages/dask/array/chunk.py:278: RuntimeWarning: invalid value encountered in cast
  return x.astype(astype_dtype, **kwargs)

Code is the following:

%%time

# Open Zarr Stores containing Echodata Objects, Lazy Load them, and Lazily Combine Echodata Objects
ed_future_list = []
for converted_file in sorted(echodata_zarr_path.glob("*.zarr")):
    ed_future = client.submit(    
        ep.open_converted,
        converted_raw_path=converted_file,
        chunks={}
    )
    ed_future_list.append(ed_future)
ed_list = client.gather(ed_future_list)
ed_combined = ep.combine_echodata(ed_list)

# Save to Zarr and offload computation to disk
ed_combined.to_zarr(
    combined_zarr_path / "ed_combined.zarr",
    overwrite=True,
    compute=True,
)

# Lazily Open Zarr
ed_combined = ep.open_converted(
    combined_zarr_path / "ed_combined.zarr",
    chunks={},
)

Using 2017 Hake Survey NWFSC EK60 raw files