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
1087160635,I_kwDOAMm_X85AzME7,6103,reindex multidimensional fill_value skipping,1191149,closed,0,,,1,2021-12-22T20:14:00Z,2021-12-22T20:17:39Z,2021-12-22T20:17:38Z,CONTRIBUTOR,,,,"**What happened**:

I started with a Dataframe that represented an identity matrix and used reindex with multiple dimensions and a fill_value. The goal was to produce a Dataset from a sparse dataframe and the identity matrix was the simplest example. The `fill_value` in reindex is defined as ""Value to use for newly missing values."" What I found was that fill_values were not applied at coordinates that were in the unique set of the any coord. For a pure identity matrix, that means fill_values were not applied anywhere (all rows are present, all cols are present). When I thin the identity matrix (skipping elements), the error is more obvious. On the rows and columns that have valid input data, the fill_value is not applied.

**What you expected to happen**:

I expected *all* new nan values to be filled with the fill value.

**Minimal Complete Verifiable Example**:

```
import numpy as np
import pandas as pd

n = 10
thin = 2

df = pd.DataFrame.from_dict([
    dict(ROW=v, COL=v, LAND=1)
    for v in np.arange(0, n, thin)
]).set_index(['ROW', 'COL'])

ds = df.to_xarray()
rds = ds.reindex(ROW=np.arange(n), COL=np.arange(n), fill_value=0)


# p = rds.LAND.plot()
# p.axes.set_facecolor('red')
# p.axes.figure.savefig('test.png')
print(rds.LAND[:])
print(rds.LAND[::thin, ::thin])
```

Output:
```
<xarray.DataArray 'LAND' (ROW: 10, COL: 10)>
array([[ 1.,  0., nan,  0., nan,  0., nan,  0., nan,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [nan,  0.,  1.,  0., nan,  0., nan,  0., nan,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [nan,  0., nan,  0.,  1.,  0., nan,  0., nan,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [nan,  0., nan,  0., nan,  0.,  1.,  0., nan,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [nan,  0., nan,  0., nan,  0., nan,  0.,  1.,  0.],
       [ 0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.,  0.]])
Coordinates:
  * ROW      (ROW) int64 0 1 2 3 4 5 6 7 8 9
  * COL      (COL) int64 0 1 2 3 4 5 6 7 8 9
<xarray.DataArray 'LAND' (ROW: 5, COL: 5)>
array([[ 1., nan, nan, nan, nan],
       [nan,  1., nan, nan, nan],
       [nan, nan,  1., nan, nan],
       [nan, nan, nan,  1., nan],
       [nan, nan, nan, nan,  1.]])
Coordinates:
  * ROW      (ROW) int64 0 2 4 6 8
  * COL      (COL) int64 0 2 4 6 8```

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

**Environment**:

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

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.12 (default, Sep 10 2021, 00:21:48) 
[GCC 7.5.0]
python-bits: 64
OS: Linux
OS-release: 5.4.144+
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: 1.12.0
libnetcdf: 4.7.4

xarray: 0.18.2
pandas: 1.1.5
numpy: 1.19.5
scipy: 1.4.1
netCDF4: 1.5.8
pydap: None
h5netcdf: None
h5py: 3.1.0
Nio: None
zarr: None
cftime: 1.5.1.1
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: 1.3.2
dask: 2.12.0
distributed: 1.25.3
matplotlib: 3.2.2
cartopy: None
seaborn: 0.11.2
numbagg: None
pint: None
setuptools: 57.4.0
pip: 21.1.3
conda: None
pytest: 3.6.4
IPython: 5.5.0
sphinx: 1.8.6


</details>
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309592370,MDU6SXNzdWUzMDk1OTIzNzA=,2025,dask ImportWarning causes pytest failure,1191149,closed,0,,,2,2018-03-29T02:01:50Z,2018-03-30T03:44:55Z,2018-03-30T03:44:55Z,CONTRIBUTOR,,,,"#### Code Sample, a copy-pastable example if possible

```bash
# Your code here
pytest -v xarray/tests/test_backends.py::NetCDF4DataTest
```
#### Problem description

Instead of passing all tests, this fails on the `test_88_character_filename_segmentation_fault` function. 

```
E               AssertionError: exception ImportWarning(""can't resolve package from __spec__ or __package__, falling back on __name__ and __path__"",) did not match pattern 'segmentation fault'
```

It oddly doesn't seem to be related to the 88 character issue. I traced this down to xarray/backends/common.py::get_scheduler where an ""ImportWarning"" is not being caught on line 49.  

#### Expected Output

Passes all tests. Adding ImportWarning to the tuple of exceptions in get_scheduler fixes the problem.

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

<details>
# Paste the output here xr.show_versions() here
>>> xr.show_versions()
/Users/barronh/anaconda3/lib/python3.6/site-packages/h5py/__init__.py:36: FutureWarning: Conversion of the second argument of issubdtype from `float` to `np.floating` is deprecated. In future, it will be treated as `np.float64 == np.dtype(float).type`.
  from ._conv import register_converters as _register_converters

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.4.final.0
python-bits: 64
OS: Darwin
OS-release: 17.4.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

xarray: 0.10.2
pandas: 0.22.0
numpy: 1.14.2
scipy: 1.0.0
netCDF4: 1.3.1
h5netcdf: None
h5py: 2.7.1
Nio: None
zarr: None
bottleneck: 1.2.1
cyordereddict: None
dask: 0.17.1
distributed: 1.21.3
matplotlib: 2.2.2
cartopy: None
seaborn: 0.8.1
setuptools: 38.4.0
pip: 9.0.1
conda: 4.5.0
pytest: 3.4.2
IPython: 6.2.1
sphinx: 1.6.6
</details>
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