Serializing a Dataset to_zarr prints error message for NetCDF

[StefanBrand]

What happened:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-30-62e3bddfeac0> in <module>
      2 ds = xr.Dataset()
      3 ds[0] = xr.DataArray()
----> 4 ds.to_zarr()

/opt/conda/envs/eurodatacube-0.22.3/lib/python3.8/site-packages/xarray/core/dataset.py in to_zarr(self, store, chunk_store, mode, synchronizer, group, encoding, compute, consolidated, append_dim, region)
   1743             encoding = {}
   1744 
-> 1745         return to_zarr(
   1746             self,
   1747             store=store,

/opt/conda/envs/eurodatacube-0.22.3/lib/python3.8/site-packages/xarray/backends/api.py in to_zarr(dataset, store, chunk_store, mode, synchronizer, group, encoding, compute, consolidated, append_dim, region)
   1452 
   1453     # validate Dataset keys, DataArray names, and attr keys/values
-> 1454     _validate_dataset_names(dataset)
   1455     _validate_attrs(dataset)
   1456 

/opt/conda/envs/eurodatacube-0.22.3/lib/python3.8/site-packages/xarray/backends/api.py in _validate_dataset_names(dataset)
    205 
    206     for k in dataset.variables:
--> 207         check_name(k)
    208 
    209 

/opt/conda/envs/eurodatacube-0.22.3/lib/python3.8/site-packages/xarray/backends/api.py in check_name(name)
    198                 )
    199         elif name is not None:
--> 200             raise TypeError(
    201                 f"Invalid name {name!r} for DataArray or Dataset key: "
    202                 "must be either a string or None for serialization to netCDF "

TypeError: Invalid name 0 for DataArray or Dataset key: must be either a string or None for serialization to netCDF files

What you expected to happen:

Print error message referring to zarr:

TypeError: Invalid name 0 for DataArray or Dataset key: must be either a string or None for serialization to zarr files

Minimal Complete Verifiable Example:

import xarray as xr
ds = xr.Dataset()
ds[0] = xr.DataArray()
ds.to_zarr()

Environment:

Output of xr.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.8.6 | packaged by conda-forge | (default, Oct  7 2020, 19:08:05) 
[GCC 7.5.0]
python-bits: 64
OS: Linux
OS-release: 4.14.177-139.253.amzn2.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8
libhdf5: 1.10.6
libnetcdf: 4.7.4

xarray: 0.16.2
pandas: 1.1.5
numpy: 1.19.4
scipy: 1.5.3
netCDF4: 1.5.5
pydap: None
h5netcdf: None
h5py: 2.10.0
Nio: None
zarr: 2.6.1
cftime: 1.3.0
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.1.5
cfgrib: None
iris: None
bottleneck: 1.3.2
dask: 2.30.0
distributed: 2.30.1
matplotlib: 3.3.3
cartopy: 0.17.0
seaborn: 0.11.0
numbagg: None
pint: None
setuptools: 49.6.0.post20201009
pip: 20.3.2
conda: None
pytest: None
IPython: 7.19.0
sphinx: 3.3.1