issues: 664611511

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
664611511 MDU6SXNzdWU2NjQ2MTE1MTE= 4261 to_zarr with append_dim behavior changed in 0.16.0 release 41797673 closed 0     4 2020-07-23T16:26:16Z 2020-11-19T15:19:48Z 2020-11-19T15:19:48Z NONE      

What happened: In version 0.15.1, calling to_zarr on a Dataset with a given append_dim would create a new zarr if it did not already exist. In version 0.16.0, this is not the case anymore: the call fails if the zarr does not exist.

Minimal Complete Verifiable Example:

```python import xarray as xr

a = xr.DataArray([1, 2], {"t": [1, 2]}, ("t",)) ds = xr.Dataset({"v": a}) ds.to_zarr("CHOOSE_PATH", append_dim="t") ```

Environment:

Output of <tt>xr.show_versions()</tt> INSTALLED VERSIONS ------------------ commit: None python: 3.7.7 (default, May 7 2020, 21:25:33) [GCC 7.3.0] python-bits: 64 OS: Linux OS-release: 4.18.0-177.el8.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_GB.UTF-8 LOCALE: en_GB.UTF-8 libhdf5: None libnetcdf: None xarray: 0.16.0 pandas: 1.0.5 numpy: 1.18.1 scipy: 1.5.0 netCDF4: None pydap: None h5netcdf: None h5py: None Nio: None zarr: 2.3.2 cftime: None nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2.14.0 distributed: 2.14.0 matplotlib: None cartopy: None seaborn: None numbagg: None pint: None setuptools: 49.2.0.post20200714 pip: 20.1.1 conda: None pytest: 5.4.3 IPython: None sphinx: None 
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   completed 13221727 issue

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