date/time conversion handles null-like objects

[pawel-wolff]

Description

This is a follow-up of the PR #999. It provides more robust checks for null-like values in the context of convertion into a data/time object.

Null-like values are:

• None
• NaN
• numpy NaT, i.e. numpy.datetime64('NaT') and numpy.timedelta64('NaT')
• pandas.NaT

Now, the following to date/time conversion routines are checking for a null-like value and return None on a null-like input:

• to_datetime()
• to_time()
• to_timedelta()

Additionally, the routines expecting numpy-type input, i.e.

• numpy_timedelta_to_timedelta()
• numpy_datetime_to_datetime()
  check for numpy NaT. Note that without such check, the conversion .astype(int) would produce a meaningless int, out of range for datetime.datetime.fromtimestamp() (see

  earthkit-data/src/earthkit/data/utils/dates.py

  Line 241 in c3e2c82

  def numpy_datetime_to_datetime(dt):

  ).

Tests covering all the above changes have been added.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.56%. Comparing base (1512d85) to head (f135d3b).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1005      +/-   ##
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+ Coverage    81.54%   81.56%   +0.02%     
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  Files          236      236              
  Lines        15493    15510      +17     
  Branches       756      756              
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+ Hits         12633    12650      +17     
  Misses        2634     2634              
  Partials       226      226              

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