issue_comments: 370043432

The failure is ``` ZarrDictStoreTest.test_explicitly_omit_fill_value_in_coord_via_encoding_kwarg _ self = <xarray.tests.test_backends.ZarrDictStoreTest testMethod=test_explicitly_omit_fill_value_in_coord_via_encoding_kwarg> def test_explicitly_omit_fill_value_in_coord_via_encoding_kwarg(self): ds = Dataset({'x': ('y', [np.pi, -np.pi])}, coords={'y': [0.0, 1.0]}) kwargs = dict(encoding={'y': {'_FillValue': None}})

  with self.roundtrip(ds, save_kwargs=kwargs) as actual:

xarray/tests/test_backends.py:721:

../../../miniconda/envs/test_env/lib/python3.6/contextlib.py:81: in enter return next(self.gen) xarray/tests/test_backends.py:1152: in roundtrip self.save(data, store_target, save_kwargs) xarray/tests/test_backends.py:1141: in save dataset.to_zarr(store=store_target, kwargs) xarray/core/dataset.py:1161: in to_zarr group=group, encoding=encoding) xarray/backends/api.py:752: in to_zarr dataset.dump_to_store(store, sync=True, encoding=encoding) xarray/core/dataset.py:1064: in dump_to_store unlimited_dims=unlimited_dims) xarray/backends/zarr.py:377: in store args, *kwargs) xarray/backends/common.py:280: in store unlimited_dims=unlimited_dims) xarray/backends/common.py:317: in set_variables name, v, check, unlimited_dims=unlimited_dims) xarray/backends/zarr.py:361: in prepare_variable variable, raise_on_invalid=check_encoding)

variable = <xarray.Variable (y: 2)> array([0., 1.]), raise_on_invalid = True def _extract_zarr_variable_encoding(variable, raise_on_invalid=False): encoding = variable.encoding.copy()

    valid_encodings = set(['chunks', 'compressor', 'filters',
                           'cache_metadata'])

    if raise_on_invalid:
        invalid = [k for k in encoding if k not in valid_encodings]
        if invalid:
            raise ValueError('unexpected encoding parameters for zarr '

                           'backend:  %r' % invalid)

E ValueError: unexpected encoding parameters for zarr backend: ['_FillValue'] ```