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Fix HelpFormatter.write usage producing spurious characters

Fix HelpFormatter.write usage producing spurious characters: a task in repo2rlenv-pr-runtime (Harbor dataset). Title: Empty output from HelpFormatter.write usage for a program without arguments

The task

**Title:** Empty output from `HelpFormatter.write_usage` for a program without arguments

Part of FineEnvs/repo2rlenv-pr-runtime.