Fail a trial if it produces empty csv file

[motus]

Pull Request

Title

Fail a trial if it produces empty csv file.
A follow-up to #998

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Description

• Fail a trial if it produces empty csv file.
• Add unit test to check for the condition.
• Small fix in split_cmdline() function to allow empty token strings (occurs in the new unit test)

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Type of Change

• 🛠️ Bug fix
• 🧪 Tests

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Testing

Run unit tests as usual

[Copilot]

Pull Request Overview

This PR enhances error handling for CSV result files by detecting and failing trials that produce empty CSV files, following up on issue #998. The changes prevent crashes when encountering malformed or empty result files.

Key Changes:

• Added exception handling for empty CSV files that would otherwise cause pandas to raise an EmptyDataError
• Fixed a potential IndexError in command line parsing when encountering empty tokens
• Added comprehensive test coverage for the new empty file scenario

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
mlos_bench/mlos_bench/environments/local/local_env.py	Added try-except block to catch EmptyDataError when reading CSV files and fail the trial gracefully
mlos_bench/mlos_bench/services/local/local_exec.py	Fixed indexing bug that could cause IndexError with empty tokens by using slice notation
mlos_bench/mlos_bench/tests/environments/local/local_env_test.py	Added new test case for zero-length CSV files and clarified existing test for CSV files with headers but no data

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[bpkroth]

Nice!