Fix cfdm.write failure for a vertical CRS that has no coordinates

[davidhassell]

Fixes #164

[codecov]

Codecov Report

Merging #165 (4cf3c08) into master (8e6ac54) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 4cf3c08 differs from pull request most recent head e16039d. Consider uploading reports for the commit e16039d to get more accurate results

@@            Coverage Diff             @@
##           master     #165      +/-   ##
==========================================
- Coverage   88.72%   88.71%   -0.00%     
==========================================
  Files         101      101              
  Lines       10806    10806              
==========================================
- Hits         9587     9586       -1     
- Misses       1219     1220       +1     

Flag	Coverage Δ
unittests	88.71% <100.00%> (-<0.01%)	⬇️

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Impacted Files	Coverage Δ
cfdm/read_write/netcdf/netcdfwrite.py	86.63% <100.00%> (ø)
cfdm/read_write/netcdf/netcdfread.py	83.45% <0.00%> (-0.05%)	⬇️

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[sadielbartholomew]

Good fix, but can we have a test to cover the case of writing a field with a vertical coordinate reference system? Nothing fails on master to indicate the issue at hand...

[davidhassell]

Hi Sadie, Fair enough! The error came from some user data, and I'll try to get a minimal reproducer we can include in the tests.

[sadielbartholomew]

Thanks for adding the new test, which passes on this PR branch but fails on master due to the issue at hand:

ERROR: test_CoordinateReference_write (__main__.CoordinateReferenceTest)
Test write when vertical CRS has no coordinates.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_CoordinateReference.py", line 61, in test_CoordinateReference_write
    cfdm.write(f, tempfile1)
  File "/home/sadie/cfdm/cfdm/read_write/write.py", line 522, in write
    netcdf.write(
  File "/home/sadie/cfdm/cfdm/decorators.py", line 171, in verbose_override_wrapper
    return method_with_verbose_kwarg(*args, **kwargs)
  File "/home/sadie/cfdm/cfdm/read_write/netcdf/netcdfwrite.py", line 4809, in write
    self._file_io_iteration(
  File "/home/sadie/cfdm/cfdm/read_write/netcdf/netcdfwrite.py", line 5089, in _file_io_iteration
    self._write_field_or_domain(f)
  File "/home/sadie/cfdm/cfdm/read_write/netcdf/netcdfwrite.py", line 3725, in _write_field_or_domain
    z_axis = self.implementation.get_construct_data_axes(
TypeError: 'NoneType' object is not subscriptable

----------------------------------------------------------------------

so captures the bug. All good!

[davidhassell]

Thank you, Sadie.