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
283345586,MDU6SXNzdWUyODMzNDU1ODY=,1792,Comparison with masked array yields object-array with nans for masked values,500246,open,0,,,3,2017-12-19T19:37:13Z,2020-10-11T13:34:25Z,,CONTRIBUTOR,,,,"#### Code Sample, a copy-pastable example if possible

```
$ cat mwe.py 
#!/usr/bin/env python3.6
import xarray
import numpy

da = xarray.DataArray(numpy.arange(5))
ma = numpy.ma.masked_array(numpy.arange(5), [True, False, False, False, True])
print(da>ma)
$ ./mwe.py 
<xarray.DataArray (dim_0: 5)>
array([nan, False, False, False, nan], dtype=object)
Dimensions without coordinates: dim_0
```

#### Problem description

A comparison between a `DataArray` and a `masked_array` results in an array with dtype `object` instead of an array with dtype `bool`.  This is problematic, because code should be able to assume that `x > y` returns something with a `bool` dtype.

#### Expected Output

I would expect the masked array to be dropped (which it is) and an array to be returned equivalent to the comparison `da>ma.data`

```
<xarray.DataArray (dim_0: 5)>
array([False, False, False, False, False], dtype=bool)
Dimensions without coordinates: dim_0
```

#### Output of ``xr.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.1.final.0
python-bits: 64
OS: Linux
OS-release: 2.6.32-696.6.3.el6.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8

xarray: 0.10.0+dev12.gf882a58
pandas: 0.21.0
numpy: 1.13.3
scipy: 1.0.0
netCDF4: 1.3.1
h5netcdf: None
Nio: None
bottleneck: 1.2.1
cyordereddict: None
dask: 0.16.0
matplotlib: 2.1.0
cartopy: None
seaborn: 0.8.1
setuptools: 38.2.4
pip: 9.0.1
conda: 4.3.16
pytest: 3.1.2
IPython: 6.1.0
sphinx: 1.6.2
None
</details>
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