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
751732952,MDU6SXNzdWU3NTE3MzI5NTI=,4612,Assigning nan to int-dtype array converts nan to int,500246,open,0,,,1,2020-11-26T17:00:45Z,2021-01-02T03:55:30Z,,CONTRIBUTOR,,,,"(I am almost sure this already exists as an issue, but I can't find the original)

**What happened**:

When assigning nan to a integer-dtype array, the nan gets incorrectly inverted to int.

**What you expected to happen**:

I expect to get a `ValueError`, like I get for pure numpy arrays.

**Minimal Complete Verifiable Example**:

```python
import xarray
import numpy
da = xarray.DataArray(numpy.array([0,1], dtype=""u8""))
da[0] = numpy.nan
print(da)
```

Gives:

```
<xarray.DataArray (dim_0: 2)>
array([9223372036854775808,                   1], dtype=uint64)
Dimensions without coordinates: dim_0
```


**Anything else we need to know?**:

In numpy the equivalent code raises `ValueError`


This is related but different from #2945.  In #2945, xarray behaves the same as numpy.  In #4612, xarray behaves differently from numpy.

**Environment**:

<details><summary>Output of <tt>xr.show_versions()</tt></summary>

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: 4.12.14-lp150.12.82-default
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8
libhdf5: 1.10.6
libnetcdf: 4.7.4

xarray: 0.16.1
pandas: 1.1.4
numpy: 1.19.4
scipy: 1.5.3
netCDF4: 1.5.4
pydap: None
h5netcdf: 0.8.1
h5py: 3.1.0
Nio: None
zarr: 2.5.0
cftime: 1.2.1
nc_time_axis: None
PseudoNetCDF: None
rasterio: 1.1.7
cfgrib: None
iris: None
bottleneck: None
dask: 2.30.0
distributed: 2.30.1
matplotlib: 3.3.2
cartopy: 0.18.0
seaborn: None
numbagg: None
pint: None
setuptools: 49.6.0.post20201009
pip: 20.2.4
conda: installed
pytest: 6.1.2
IPython: 7.19.0
sphinx: 3.3.0


</details>
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410317757,MDU6SXNzdWU0MTAzMTc3NTc=,2772,Should xarray allow assigning a masked constant?,500246,open,0,,,1,2019-02-14T14:10:20Z,2019-02-15T20:24:44Z,,CONTRIBUTOR,,,,"Currently, `ds['a'] = ((), ma.masked)` where `ds` is an `xarray.Dataset` gives `ValueError: Could not convert tuple of form (dims, data[, attrs, encoding]): ((), masked) to Variable.`, whereas `ds['a'] = (), ma.MaskedArray(0.0, True)` works (it sets the indicated value to NaN).  Should assigning `ma.masked` be equivalent to assigning `ma.MaskedArray(0.0, True)`, or are there good reasons for the difference in behaviour?","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/2772/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,issue