What happened?

```python with xr.set_options(display_style="text", use_flox=False): with xr.set_options(use_flox=False): display( xr.DataArray( data=np.array([np.nan, 1, 1, np.nan, 1, 1]), dims="x", coords={"labels": ("x", np.array([1, 2, 3, 1, 2, 3]))}, ) .groupby("labels") .sum() )

with xr.set_options(use_flox=True):
    display(
        xr.DataArray(
            data=np.array([np.nan, 1, 1, np.nan, 1, 1]),
            dims="x",
            coords={"labels": ("x", np.array([1, 2, 3, 1, 2, 3]))},
        )
        .groupby("labels")
        .sum()
    )

```

```

without flox

<xarray.DataArray (labels: 3)> array([0., 2., 2.]) Coordinates: * labels (labels) int64 1 2 3

with flox

<xarray.DataArray (labels: 3)> array([nan, 2., 2.]) Coordinates: * labels (labels) int64 1 2 3 ```

What did you expect to happen?

The same answer. We should set min_count=0 when min_count is None

Minimal Complete Verifiable Example

No response

MVCE confirmation

• [ ] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• [ ] Complete example — the example is self-contained, including all data and the text of any traceback.
• [ ] Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• [ ] New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

No response

Anything else we need to know?

No response

Environment