fix: Ensure adding RailsConfig objects handles None values

[JashG]

Description

The RailsConfig class allows for adding two config objects. This MR addresses two edge cases where this function throws an error.

I ran into this error upstream using the NeMo Guardrails service. Internally, the /v1/chat/completions endpoint invokes RailsConfig.__add__ when given multiple config IDs. I ran into these two errors when attempting to use this endpoint with multiple sample configs.

Related Issue(s)

• Fixes bug: RailsConfig throws error when adding configs #1327

Checklist

• I've read the CONTRIBUTING guidelines.
• I've updated the documentation if applicable.
• I've added tests if applicable.
• [] @mentions of the person or team responsible for reviewing proposed changes.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.61%. Comparing base (6ba7832) to head (dfb4484).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1328      +/-   ##
===========================================
+ Coverage    70.58%   70.61%   +0.02%     
===========================================
  Files          161      161              
  Lines        16291    16303      +12     
===========================================
+ Hits         11499    11512      +13     
+ Misses        4792     4791       -1     

Flag	Coverage Δ
python	70.61% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
nemoguardrails/rails/llm/config.py	90.53% <100.00%> (+0.19%)	⬆️

... and 1 file with indirect coverage changes

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[Copilot]

Pull Request Overview

This PR addresses edge cases in the RailsConfig.__add__ method where adding two config objects with None values for prompts or config_path would cause errors. The fix ensures proper handling of None values when merging configs and includes comprehensive test coverage for the addition functionality.

• Adds null-safety checks for prompts field in validation methods
• Handles None values for config_path when joining configuration paths
• Introduces comprehensive test suite for RailsConfig addition functionality

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
nemoguardrails/rails/llm/config.py	Adds null-safety checks for prompts field and config_path handling
tests/rails/llm/test_config.py	Adds comprehensive test coverage for RailsConfig addition scenarios

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[Pouyanpi]

Thank you @JashG for fixing this bug 👍🏻 can you gpg sign your commit following contributing guidelines?

[JashG]

@Pouyanpi Done!

[Pouyanpi]

LGTM! Thank you @JashG 👍🏻