Fix: Make ARRIVAL_TIME validation consistent and remove invalid sentinel default

[Agarwalchetan]

Related Issue / Discussion:

Fixes Issue #145

Changes:

• Modified WeatherRoutingTool/config.py

  • Changed ARRIVAL_TIME to Optional[datetime] = None
  • Updated datetime validation logic to handle None correctly
  • Corrected error messages to reference the validated field name
  • Replaced sentinel string comparisons with None checks in check_speed_determination
  • Added backward compatibility for legacy sentinel string ('9999-99-99T99:99Z')

• Modified WeatherRoutingTool/tests/test_config.py

  • Added unit tests covering:

    • ARRIVAL_TIME omitted
    • Both ARRIVAL_TIME and BOAT_SPEED specified
    • Neither specified
    • Invalid datetime format validation

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Further Details:

Summary:

Previously, ARRIVAL_TIME was typed as datetime but used the string sentinel '9999-99-99T99:99Z' as a default value. This string is not a valid datetime and required string comparisons in validation logic.

Additionally, the datetime validator emitted error messages that referenced only DEPARTURE_TIME, even when validating ARRIVAL_TIME.

This PR:

• Replaces the sentinel string with None using Optional[datetime]
• Updates validation logic to rely on semantic None checks
• Corrects error messages to reflect the validated field
• Preserves backward compatibility by treating the legacy sentinel string as an alias for “unset”
• Adds unit tests to ensure consistent behavior

Behavioral outcome:

• Validation succeeds when ARRIVAL_TIME is omitted
• Validation fails if both ARRIVAL_TIME and BOAT_SPEED are specified
• Validation fails if neither is specified
• Error messages correctly reference the validated field

This improves type consistency, simplifies validation logic, and maintains existing functionality.

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Dependencies:

No new dependencies introduced.

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PR Checklist:

In the context of this PR, I:

• have (already previously) filled the 52North Contributor License Agreement and received positive feedback on this matter
• have filled the 52North Contributor License Agreement and am waiting for feedback
• provide unit tests embedded in the WRT test framework (WeatherRoutingTool/tests) that allow the simple testing of the new/modified functionalities. All (previous and new) unit tests execute without new error messages.
• ensure that the code formatter runs without errors/warnings
• ensure that my changes follow the WRT’s guidelines for contributing at the time of the contribution

Please consider that PRs which do not meet the requirements specified in the checklist will not be evaluated. Also, PRs with no activities will be closed after a reasonable amount of time.

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