CIDC-876 change file derivation to return None instead of erroring when not defined

[scvannost]

Why

• CIDC-876 derive_files_from_... cloud functions throw errors when no derivation is implemented

How

• Remove hardcoded raise

Remarks

• will need to handle None return in upload_postprocessing CFn
• no current test for error

Checklist

Please include and complete the following checklist. You can mark an item as complete with the - [x] prefix:

• Tests - Added unit tests for new code, regression tests for bugs and updated the integration tests if required
• Formatting & Linting - black and flake8 have been used to ensure styling guidelines are met
• Type Annotations - All new code has been type annotated in the function signatures using type hints
• Docstrings - Docstrings have been provided for functions
• Documentation - Documentation in docs/ has be regenerated and README and CHANGELOG have been updated to explain major changes & new features
• Package version - Manually bumped the Schemas package version in cidc_schemas/__init__.py

[codeclimate]

Code Climate has analyzed commit 15923f5 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 94.5% (0.0% change).

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